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A geographic information system (GIS) is a type of
database In , a database is an organized collection of stored and accessed electronically from a . Where databases are more complex they are often developed using formal techniques. The (DBMS) is the that interacts with s, applications, and the data ...

database
containing
geographic data Geographic data and information is defined in the ISO/TC 211 series of standards as data and information having an implicit or explicit association with a location relative to Earth (a geographic location or geographic position). It is also calle ...
(that is, descriptions of phenomena for which location is relevant), combined with
software tools A programming tool or software development tool is a that s use to create, debug, maintain, or otherwise support other programs and applications. The term usually refers to relatively simple programs, that can be combined to accomplish a task, mu ...
for managing,
analyzing Analysis is the process of breaking a complexity, complex topic or Substance theory, substance into smaller parts in order to gain a better understanding of it. The technique has been applied in the study of mathematics and logic since before Ari ...
, and visualizing those data. In a broader sense, one may consider such a system to also include human users and support staff, procedures and workflows, body of knowledge of relevant concepts and methods, and institutional organizations. The uncounted plural, ''geographic information systems'', also abbreviated GIS, is the most common term for the industry and profession concerned with these systems, and is thus roughly synonymous with
geospatial Geographic data and information is defined in the ISO/TC 211 series of standards as data and information having an implicit or explicit association with a location relative to Earth (a geographic location or geographic position). It is also calle ...
and
geoinformatics Geoinformatics is the science and the technology which develops and uses information science Information science (also known as information studies) is an academic field which is primarily concerned with analysis, collection, Categorization, c ...
. Geographic information science, the academic discipline that studies these systems and their underlying geographic principles, may also be abbreviated as GIS, but the unambiguous GIScience is more common. Geographic information systems are utilized in multiple technologies, processes, techniques and methods. They are attached to various operations and numerous applications, that relate to: engineering, planning, management, transport/logistics, insurance, telecommunications, and business. For this reason, GIS and
location intelligence In business intelligence Business intelligence (BI) comprises the strategies and technologies used by enterprises for the data analysis Data analysis is a process of inspecting, Data cleansing, cleansing, Data transformation, transforming, and ...
applications are at the foundation of location-enabled services, that rely on geographic analysis and visualization. GIS provides the capability to relate previously unrelated information, through the use of location as the "key index variable". Locations and extents that are found in the Earth's
spacetime In , spacetime is any which fuses the and the one of into a single . can be used to visualize effects, such as why different observers perceive differently where and when events occur. Until the 20th century, it was assumed that the three ...
, are able to be recorded through the date and time of occurrence, along with x, y, and z
coordinate In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space t ...

coordinate
s; representing,
longitude Longitude (, ) is a geographic coordinate A geographic coordinate system (GCS) is a coordinate system associated with position (geometry), positions on Earth (geographic position). A GCS can give positions: *as Geodetic coordinates, ...

longitude
(''x''),
latitude In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use the ...

latitude
(''y''), and
elevation The elevation of a geographic Geography (from Greek: , ''geographia'', literally "earth description") is a field of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...
(''z''). All Earth-based, spatial–temporal, location and extent references, should be relatable to one another, and ultimately, to a "real" physical location or extent. This key characteristic of GIS, has begun to open new avenues of scientific inquiry and studies.


History and development

While digital GIS dates to the mid-1960s, when
Roger Tomlinson Roger F. Tomlinson, (17 November 1933 – 7 February 2014) was an English geographer and the primary originator of modern computerised geographic information systems (GIS), and has been acknowledged as the "father of GIS." Biography Dr. Tomlin ...
first coined the phrase "geographic information system", many of the geographic concepts and methods that GIS automates date back decades earlier. One of the first known instances in which spatial analysis was used came from the field of
epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants In mathematics, the determinant is a Scalar (mathematics), scalar value that is a function (mathematics), function of the entries of a ...
in the "''Rapport sur la marche et les effets du choléra dans Paris et le département de la
Seine ) , mouth_location = Le Havre Le Havre (, ; nrf, Lé Hâvre) is an urban French Communes of France, commune and city in the Seine-Maritime Departments of France, department in the Normandy (administrative region), Normandy region of nor ...

Seine
''" (1832). French geographer and
cartographer Cartography (; from Greek χάρτης ''chartēs'', "papyrus, sheet of paper, map"; and γράφειν ''graphein'', "write") is the study and practice of making and using maps. Combining science Science (from the Latin word ''scienti ...
,
Charles Picquet Charles is a masculine given name predominantly found in English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early med ...
created a map outlining the forty-eight Districts in
Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, most populous city of France, with an estimated population of 2,175,601 residents , in an area of more than . Since the 17th century, Paris ha ...

Paris
, using
halftone Halftone is the reprographicReprography is the reproduction of graphics through mechanical or electrical means, such as photography or xerography. Reprography is commonly used in catalogs and archives, as well as in the architectural reprography ...
color gradients, to provide a visual representation for the number of reported deaths due to
cholera Cholera is an infection An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host A host is a person responsible for guests at an event or for providing hospit ...

cholera
per every 1,000 inhabitants. In 1854,
John Snow John Snow (15 March 1813 – 16 June 1858) was an English physician and a leader in the development of anaesthesia and medical hygiene. He is considered one of the founders of modern epidemiology, in part because of his work in tracing the s ...

John Snow
, an epidemiologist and physician, was able to determine the source of a cholera outbreak in
London London is the and of and the . It stands on the in south-east England at the head of a down to the , and has been a major settlement for two millennia. The , its ancient core and financial centre, was founded by the as ' and retains b ...

London
through the use of spatial analysis. Snow achieved this through plotting the residence of each casualty on a map of the area, as well as the nearby water sources. Once these points were marked, he was able to identify the water source within the cluster that was responsible for the outbreak. This was one of the earliest successful uses of a geographic methodology in pinpointing the source of an outbreak in epidemiology. While the basic elements of
topography Topography is the study of the forms and features of land surfaces. The topography of an area could refer to the surface forms and features themselves, or a description (especially their depiction in maps). Topography is a field of geoscience ...
and theme existed previously in
cartography Cartography (; from χάρτης ''chartēs'', "papyrus, sheet of paper, map"; and γράφειν ''graphein'', "write") is the study and practice of making and using s. Combining , , and technique, cartography builds on the premise that rea ...
, Snow's map was unique due to his use of cartographic methods, not only to depict, but also to analyze clusters of geographically dependent phenomena. The early 20th century saw the development of
photozincographyPhotozincography, sometimes referred to as heliozincography but essentially the same process, known commercially as zinco, is the photographic process developed by Sir Henry James FRS (1803–1877) in the mid-nineteenth century. This method en ...
, which allowed maps to be split into layers, for example one layer for vegetation and another for water. This was particularly used for printing contours – drawing these was a labour-intensive task but having them on a separate layer meant they could be worked on without the other layers to confuse the draughtsman. This work was originally drawn on glass plates but later
plastic film Plastic film is a thin continuous polymeric material. Thicker plastic material is often called a "sheet". These thin plastic Plastics are a wide range of synthetic polymers, synthetic or semi-synthetic materials that use polymers as a main i ...
was introduced, with the advantages of being lighter, using less storage space and being less brittle, among others. When all the layers were finished, they were combined into one image using a large process camera. Once color printing came in, the layers idea was also used for creating separate printing plates for each color. While the use of layers much later became one of the main typical features of a contemporary GIS, the photographic process just described is not considered to be a GIS in itself – as the maps were just images with no database to link them to. Two additional developments are notable in the early days of GIS: Ian McHarg's publication "''Design with Nature"'' and its map overlay method and the introduction of a street network into the U.S. Census Bureau's DIME (Dual Independent Map Encoding) system.
Computer hardware Computer hardware includes the physical parts of a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations ...

Computer hardware
development spurred by
nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics and nucl ...
research led to general-purpose computer "mapping" applications by the early 1960s. In 1960 the world's first true operational GIS was developed in
Ottawa, Ontario Ottawa (, ; Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are c ...
, Canada, by the federal Department of Forestry and Rural Development. Developed by Dr.
Roger Tomlinson Roger F. Tomlinson, (17 November 1933 – 7 February 2014) was an English geographer and the primary originator of modern computerised geographic information systems (GIS), and has been acknowledged as the "father of GIS." Biography Dr. Tomlin ...
, it was called the
Canada Geographic Information System {{Unreferenced, date=October 2012 The Canada Geographic Information System (CGIS) was an early geographic information system A geographic information system (GIS) is a conceptualized framework that provides the ability to capture and analyze s ...
(CGIS) and was used to store, analyze, and manipulate data collected for the Canada Land Inventory, an effort to determine the land capability for rural Canada by mapping information about
soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms tha ...

soil
s, agriculture, recreation, wildlife,
waterfowl Anseriformes is an order (biology), order of birds that comprise about 180 living species in three families: Anhimidae (the 3 screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which includes over 170 species of water ...
,
forestry Forestry is the science and craft of creating, managing, planting, using, conserving and repairing forest A forest is an area of land dominated by s. Hundreds of definitions of forest are used throughout the world, incorporating fac ...
and land use at a scale of 1:50,000. A rating classification factor was also added to permit analysis. CGIS was an improvement over "computer mapping" applications as it provided capabilities for data storage, overlay, measurement, and
digitizing DigitizationDefinition of digitization
at WhatIs.com
is the process of converting ...
/scanning. It supported a national coordinate system that spanned the continent, coded lines as
arcsARCS may stand for: * Alabama Regional Communications System, a radio/alert notification communications district in the State of Alabama * Associate of the Royal College of Science * ARCS (computing), a firmware bootloader * Admiralty Raster Chart Se ...

arcs
having a true embedded
topology s, which have only one surface and one edge, are a kind of object studied in topology. In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structu ...

topology
and it stored the attribute and locational information in separate files. As a result of this, Tomlinson has become known as the "father of GIS", particularly for his use of overlays in promoting the spatial analysis of convergent geographic data. CGIS lasted into the 1990s and built a large digital land resource database in Canada. It was developed as a
mainframe A pair of IBM mainframes. On the left is the IBM z Systems z13. On the right is the IBM LinuxONE Rockhopper.">IBM_LinuxONE.html" ;"title="IBM z Systems z13. On the right is the IBM LinuxONE">IBM z Systems z13. On the right is the IBM LinuxONE R ...
-based system in support of federal and provincial resource planning and management. Its strength was continent-wide analysis of complex
dataset A data set (or dataset) is a collection of data Data (; ) are individual facts, statistics, or items of information, often numeric. In a more technical sense, data are a set of values of qualitative property, qualitative or quantity, quantita ...
s. The CGIS was never available commercially. In 1964 Howard T. Fisher formed the Laboratory for Computer Graphics and Spatial Analysis at the
Harvard Graduate School of Design The Harvard Graduate School of Design (GSD) is a graduate school File:CCMDonation49.JPG, Student receives degree from the Monterrey Institute of Technology and Higher Education, Mexico City, 2013 A graduate school (sometimes shortened to grad ...
(LCGSA 1965–1991), where a number of important theoretical concepts in spatial data handling were developed, and which by the 1970s had distributed seminal software code and systems, such as SYMAP, GRID, and ODYSSEY, to universities, research centers and corporations worldwide. These programs were the first examples of general purpose GIS software that was not developed for a particular installation, and was very influential on future commercial software, such as
Esri Esri (; Environmental Systems Research Institute) is an international supplier of geographic information system (GIS) software, web GIS and geodatabase management applications. The company is headquartered in Redlands, California, Redlands, Cali ...
ARC/INFO, released in 1983. By the late 1970s two public domain GIS systems (
MOSS Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...
and
GRASS GIS ''Geographic Resources Analysis Support System'' (commonly termed ''GRASS GIS'') is a geographic information system (GIS) software suite used for geospatial data management and analysis, image processing, producing graphics and maps, spatial and t ...
) were in development, and by the early 1980s, M&S Computing (later
Intergraph Intergraph Corporation was an American software development and services company, which now forms part of Hexagon AB Hexagon AB is a global technology group headquartered in Sweden. The operation is focused on precision measuring technologies and ...

Intergraph
) along with Bentley Systems Incorporated for the
CAD Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve comm ...
 platform, Environmental Systems Research Institute (
ESRI Esri (; Environmental Systems Research Institute) is an international supplier of geographic information system (GIS) software, web GIS and geodatabase management applications. The company is headquartered in Redlands, California, Redlands, Cali ...
), CARIS (Computer Aided Resource Information System), and ERDAS (Earth Resource Data Analysis System) emerged as commercial vendors of GIS software, successfully incorporating many of the CGIS features, combining the first generation approach to separation of spatial and attribute information with a second generation approach to organizing attribute data into database structures. In 1986, Mapping Display and Analysis System (MIDAS), the first desktop GIS product was released for the
DOS DOS (, ) is a platform-independent acronym for disk operating system which later became a common shorthand for disk-based operating systems on IBM PC compatible IBM PC compatible computers are similar to the original IBM Personal Computer, IB ...

DOS
operating system. This was renamed in 1990 to MapInfo for Windows when it was ported to the
Microsoft Windows Microsoft Windows, commonly referred to as Windows, is a group of several families, all of which are developed and marketed by . Each family caters to a certain sector of the computing industry. Active Microsoft Windows families include an ...
platform. This began the process of moving GIS from the research department into the business environment. By the end of the 20th century, the rapid growth in various systems had been consolidated and standardized on relatively few platforms and users were beginning to explore viewing GIS data over the
Internet The Internet (or internet) is the global system of interconnected s that uses the (TCP/IP) to communicate between networks and devices. It is a ' that consists of private, public, academic, business, and government networks of local to ...

Internet
, requiring data format and transfer standards. More recently, a growing number of free, open-source GIS packages run on a range of operating systems and can be customized to perform specific tasks. The major trend of the 21st Century has been the integration of GIS capabilities with other Information technology and
Internet The Internet (or internet) is the global system of interconnected s that uses the (TCP/IP) to communicate between networks and devices. It is a ' that consists of private, public, academic, business, and government networks of local to ...

Internet
infrastructure, such as
relational database A relational database is a digital based on the of data, as proposed by in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relational database systems have an option of using the (S ...
s,
cloud computing Cloud computing is the on-demand availability of computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operatio ...

cloud computing
,
software as a service Software as a service (SaaS ) is a software licensing and software delivery, delivery model in which software is licensed on a subscription basis and is centrally Internet hosting service, hosted. It is sometimes referred to as "on-demand software" ...
(SAAS), and
mobile computing Mobile computing is human–computer interaction in which a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of o ...
.


GIS software

The distinction must be made between a singular ''geographic information system'', which is a single installation of software and data for a particular use, along with associated hardware, staff, and institutions (e.g., the GIS for a particular city government); and ''GIS software'', a general-purpose application program that is intended to be used in many individual geographic information systems in a variety of application domains. Starting in the late 1970s, many software packages have been created specifically for GIS applications, including commercial programs such as
Esri Esri (; Environmental Systems Research Institute) is an international supplier of geographic information system (GIS) software, web GIS and geodatabase management applications. The company is headquartered in Redlands, California, Redlands, Cali ...
ArcGIS ArcGIS is a geographic information system (GIS) for working with maps and geographic information maintained by the Esri, Environmental Systems Research Institute (Esri). It is used for creating and using maps, compiling geographic data, analyzing m ...
and
MapInfo Professional MapInfo Pro is a desktop geographic information system (GIS) software product produced by Precisely (formerly: Pitney Bowes Software and MapInfo Corporation) and used for Cartography, mapping and location analysis. MapInfo Pro allows users to visua ...
and open source programs such as
QGIS QGIS (until 2013 known as Quantum GIS) is a free and open-source cross-platform In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of al ...
and
GRASS GIS ''Geographic Resources Analysis Support System'' (commonly termed ''GRASS GIS'') is a geographic information system (GIS) software suite used for geospatial data management and analysis, image processing, producing graphics and maps, spatial and t ...
. These and other ''desktop GIS applications'' include a full suite of capabilities for entering, managing, analyzing, and visualizing geographic data, and are designed to be used on their own. Starting in the late 1990s with the emergence of the
Internet The Internet (or internet) is the global system of interconnected s that uses the (TCP/IP) to communicate between networks and devices. It is a ' that consists of private, public, academic, business, and government networks of local to ...

Internet
, ''server GIS'' has been developed as another mechanism for providing GIS capabilities. This is standalone software installed on a server, similar to other server software such as
HTTP server A web server is computer software and underlying hardware that accepts requests via Hypertext Transfer Protocol, HTTP, the network protocol created to distribute web pages, or its secure variant HTTPS. A user agent, commonly a web browser or web ...
s and
relational database management system A relational database is a digital database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relational database system ...
s, enabling clients to have access to GIS data and processing tools without having to install specialized desktop software, often by accessing the server through a web browser. This strategy has been extended through the development of cloud-based GIS platforms such a
ArcGIS Online
and GIS-specialized
Software as a service Software as a service (SaaS ) is a software licensing A software license is a legal instrument (usually by way of contract law A contract is a legally binding agreement that defines and governs the rights and duties between or among its P ...
(SAAS). An alternative approach is to integrate of some or all of these capabilities into other software or information technology architectures. One example is a spatial extension to Object-relational database software, which defines a geometry datatype so that spatial data can be stored in relational tables, and extensions to
SQL SQL ( ''S-Q-L'', "sequel"; Structured Query Language) is a domain-specific languageA domain-specific language (DSL) is a computer languageA computer language is a method of communication with a computer A computer is a machine that can b ...

SQL
for spatial analysis operations such as overlay. Another example is the proliferation of geospatial libraries and
application programming interface In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and so ...
s (e.g.,
GDAL The Geospatial Data Abstraction Library (GDAL) is a computer software Library (computer science), library for reading and writing Raster graphics, raster and Vector graphics, vector GIS file formats, geospatial data formats, and is released under ...
, Leaflet,
D3.js D3.js (also known as D3, short for Data-Driven Documents) is a JavaScript JavaScript (), often abbreviated JS, is a programming language A programming language is a formal language In mathematics Mathematics (from Ancient Gree ...
) that extend programming languages to enable the incorporation of GIS data and processing into custom software, including
web mapping A Web mapping or an online mapping is the process of using the maps delivered by Geographic Information Systems, geographic information systems (GIS) on the Internet, more specifically in the World Wide Web (WWW). A web map or an online map is bo ...
sites and
location-based service A location-based service (LBS) is a general term denoting software services which use geographic data and information to provide services or information to users. LBS can be used in a variety of contexts, such as health, indoor object detection, ob ...
s in
smartphone A smartphone is a portable device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can per ...

smartphone
s.


Geospatial data management

The core of any GIS is a
database In , a database is an organized collection of stored and accessed electronically from a . Where databases are more complex they are often developed using formal techniques. The (DBMS) is the that interacts with s, applications, and the data ...

database
that contains representations of geographic phenomena, modeling their ''geometry'' (location and shape) and their ''properties'' or ''attributes''. A GIS database may be stored in a variety of forms, such as a collection of separate data files or a single spatially-enabled
relational database A relational database is a digital based on the of data, as proposed by in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relational database systems have an option of using the (S ...
. Collecting and managing these data usually comprise the bulk of the time and financial resources of a project, far more than other aspects such as analysis and mapping.


Aspects of geographic data

GIS uses spatio-temporal (
space-time In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...
) location as the key index variable for all other information. Just as a relational database containing text or numbers can relate many different tables using common key index variables, GIS can relate otherwise unrelated information by using location as the key index variable. The key is the location and/or extent in space-time. Any variable that can be located spatially, and increasingly also temporally, can be referenced using a GIS. Locations or extents in Earth space–time may be recorded as dates/times of occurrence, and x, y, and z
coordinate In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space t ...

coordinate
s representing,
longitude Longitude (, ) is a geographic coordinate A geographic coordinate system (GCS) is a coordinate system associated with position (geometry), positions on Earth (geographic position). A GCS can give positions: *as Geodetic coordinates, ...

longitude
,
latitude In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use the ...

latitude
, and
elevation The elevation of a geographic Geography (from Greek: , ''geographia'', literally "earth description") is a field of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...
, respectively. These GIS coordinates may represent other quantified systems of temporo-spatial reference (for example, film frame number, stream gage station, highway mile-marker, surveyor benchmark, building address, street intersection, entrance gate, water depth sounding, POS or
CAD Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve comm ...
drawing origin/units). Units applied to recorded temporal-spatial data can vary widely (even when using exactly the same data, see
map projection In cartography, a map projection is a way to flatten a globe's surface into a plane in order to make a map. This requires a systematic transformation of the latitudes and longitudes of locations from the Surface (mathematics), surface of the globe ...
s), but all Earth-based spatial–temporal location and extent references should, ideally, be relatable to one another and ultimately to a "real" physical location or extent in space–time. Related by accurate spatial information, an incredible variety of real-world and projected past or future data can be analyzed, interpreted and represented. This key characteristic of GIS has begun to open new avenues of scientific inquiry into behaviors and patterns of real-world information that previously had not been systematically
correlated In , correlation or dependence is any statistical relationship, whether or not, between two s or . In the broadest sense correlation is any statistical association, though it actually refers to the degree to which a pair of variables are rel ...

correlated
.


Data modeling

GIS data represents phenomena that exist in the real world, such as roads, land use, elevation, trees, waterways, and states. The most common types of phenomena that are represented in data can be divided into two conceptualizations: discrete objects (e.g., a house, a road) and continuous fields (e.g., rainfall amount or population density). } Other types of geographic phenomena, such as events (e.g.,
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a global war A world war is "a war War is an intense armed conflict between states State may refer to: Arts, entertainment, and media Literatur ...
), processes (e.g.,
suburbanization pattern in the US Suburbanization is a population shift from central urban area An urban area, or built-up area, is a human settlement with a high population density and infrastructure of built environment. Urban areas are created through ...
), and masses (e.g.,
soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms tha ...

soil
) are represented less commonly or indirectly, or are modeled in analysis procedures rather than data. Traditionally, there are two broad methods used to store data in a GIS for both kinds of abstractions mapping references:
raster images file:Rgb-raster-image.svg, upright=1, The Smiley, smiley face in the top left corner is a raster image. When enlarged, individual pixels appear as squares. Enlarging further, each pixel can be analyzed, with their colors constructed through comb ...
and
vector Vector may refer to: Biology *Vector (epidemiology) In epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and risk factor, determinants of health and disease conditions in defined pop ...
. Points, lines, and polygons represent vector data of mapped location attribute references. A new hybrid method of storing data is that of identifying point clouds, which combine three-dimensional points with
RGB s The RGB color model is an additive color, additive color model A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components. When ...

RGB
information at each point, returning a " 3D color image". GIS thematic maps then are becoming more and more realistically visually descriptive of what they set out to show or determine.


Data acquisition

GIS data acquisition includes several methods for gathering spatial data into a GIS database, which can be grouped into three categories: ''primary data capture'', the direct measurement phenomena in the field (e.g.,
remote sensing Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ ''In situ'' (; often not italicized in English) is a Latin Latin (, or , ) is a class ...

remote sensing
, the
global positioning system The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government The federal government of the United States (U.S. federal government or U.S. governme ...
); ''secondary data capture'', the extraction of information from existing sources that are not in a GIS form, such as paper maps, through
digitization DigitizationTech Target. (2011, April). Definition: digitization. ''WhatIs.com''. Retrieved December 15, 2021, from https://whatis.techtarget.com/definition/digitization is the process of converting information into a digital Digital usuall ...

digitization
; and '' data transfer'', the copying of existing GIS data from external sources such as government agencies and private companties. All of these methods can consume significant time, finances, and other resources.


Primary data capture

Survey Survey may refer to: Statistics and human research * Statistical survey Survey methodology is "the study of survey methods". As a field of applied statistics concentrating on Survey (human research), human-research surveys, survey methodology s ...

Survey
data can be directly entered into a GIS from digital data collection systems on survey instruments using a technique called coordinate geometry (COGO). Positions from a global navigation satellite system (
GNSS A satellite navigation or satnav system is a system that uses satellite alt=, A full-size model of the Earth observation satellite ERS 2 ">ERS_2.html" ;"title="Earth observation satellite ERS 2">Earth observation satellite ERS 2 In the ...
) like
Global Positioning System The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government The federal government of the United States (U.S. federal government or U.S. governme ...
can also be collected and then imported into a GIS. A current trend in data collection gives users the ability to utilize field computers with the ability to edit live data using wireless connections or disconnected editing sessions. This has been enhanced by the availability of low-cost mapping-grade GPS units with decimeter accuracy in real time. This eliminates the need to post process, import, and update the data in the office after fieldwork has been collected. This includes the ability to incorporate positions collected using a
laser rangefinder and elevation The elevation of a geographic location (geography), location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational eq ...
. New technologies also allow users to create maps as well as analysis directly in the field, making projects more efficient and mapping more accurate. data also plays an important role in data collection and consist of sensors attached to a platform. Sensors include cameras, digital scanners and
lidar Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object with a laser A laser is a device that emits light Light or visible light is electromagnetic radiati ...
, while platforms usually consist of aircraft and
satellite In the context of spaceflight Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either human spaceflight, with or uncrewed spaceflight, without humans on board. Most spaceflight ...

satellite
s. In England in the mid 1990s, hybrid kite/balloons called helikites first pioneered the use of compact airborne digital cameras as airborne geo-information systems. Aircraft measurement software, accurate to 0.4 mm was used to link the photographs and measure the ground. Helikites are inexpensive and gather more accurate data than aircraft. Helikites can be used over roads, railways and towns where
unmanned aerial vehicle , a hunter-killer surveillance UAV , rotorcraft A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft An aircraft is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters th ...

unmanned aerial vehicle
s (UAVs) are banned. Recently aerial data collection has become more accessible with
miniature UAV of the Turkish Land Forces of the German Army A miniature UAV, small UAV (SUAV), or drone is an unmanned aerial vehicle small enough to be man-portable. Miniature UAVs range from micro air vehicles (MAVs) that can be carried by an infantryman, ...
s and drones. For example, the Aeryon Scout was used to map a 50-acre area with a
ground sample distanceIn remote sensing, ground sample distance (GSD) in a digital photo (such as an orthophoto) of the ground from air or space is the distance between pixel centers measured on the ground. For example, in an image with a one-meter GSD, adjacent pixels im ...
of in only 12 minutes. The majority of digital data currently comes from
photo interpretation Photographic interpretation is “the act of examining photographic images for the purpose of identifying objects and judging their significance” (Colwell, 1997). This mainly refers to its usage in military aerial reconnaissance using photographs ...

photo interpretation
of aerial photographs. Soft-copy workstations are used to digitize features directly from stereo pairs of digital photographs. These systems allow data to be captured in two and three dimensions, with elevations measured directly from a stereo pair using principles of
photogrammetry Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant ima ...
. Analog aerial photos must be scanned before being entered into a soft-copy system, for high-quality digital cameras this step is skipped. Satellite
remote sensing Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ ''In situ'' (; often not italicized in English) is a Latin Latin (, or , ) is a class ...

remote sensing
provides another important source of spatial data. Here satellites use different sensor packages to passively measure the reflectance from parts of the
electromagnetic spectrum The electromagnetic spectrum is the range of frequency, frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energy, photon energies. The electromagnetic spectrum covers electromagnetic waves with f ...

electromagnetic spectrum
or radio waves that were sent out from an active sensor such as radar. Remote sensing collects raster data that can be further processed using different bands to identify objects and classes of interest, such as land cover.


Secondary data capture

The most common method of data creation is
digitization DigitizationTech Target. (2011, April). Definition: digitization. ''WhatIs.com''. Retrieved December 15, 2021, from https://whatis.techtarget.com/definition/digitization is the process of converting information into a digital Digital usuall ...
, where a
hard copy In information handling, the U.S. Federal Standard 1037C Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms, is a United States The United States of America (USA), commonly known as the United State ...
map or survey plan is transferred into a digital medium through the use of a CAD program, and geo-referencing capabilities. With the wide availability of ortho-rectified imagery (from satellites, aircraft, Helikites and UAVs), heads-up digitizing is becoming the main avenue through which geographic data is extracted. Heads-up digitizing involves the tracing of geographic data directly on top of the aerial imagery instead of by the traditional method of tracing the geographic form on a separate digitizing tablet (heads-down digitizing). Heads-down digitizing, or manual digitizing, uses a special magnetic pen, or stylus, that feeds information into a computer to create an identical, digital map. Some tablets use a mouse-like tool, called a puck, instead of a stylus. The puck has a small window with cross-hairs which allows for greater precision and pinpointing map features. Though heads-up digitizing is more commonly used, heads-down digitizing is still useful for digitizing maps of poor quality. Existing data printed on paper or PET film maps can be
digitized DigitizationDefinition of digitization
at WhatIs.com
is the process of converting ...

digitized
or scanned to produce digital data. A digitizer produces
vector Vector may refer to: Biology *Vector (epidemiology) In epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and risk factor, determinants of health and disease conditions in defined pop ...
data as an operator traces points, lines, and polygon boundaries from a map. Scanning a map results in raster data that could be further processed to produce vector data.
Web mining Web mining is the application of data mining techniques to discover patterns from the World Wide Web upright=1.35, A global map of the web index for countries in 2014 The World Wide Web (WWW), commonly known as the Web, is an informati ...
is a novel method of collecting spatial data. Researchers build a web crawler application to aggregate required spatial data from
the web The World Wide Web (WWW), commonly known as the Web, is an information system where documents and other web resources are identified by URL, Uniform Resource Locators (URLs, such as ), which may be interlinked by hyperlinks, and are acce ...
. For example, the exact geo-location or the neighborhood of apartments can be collected from online real estate listing websites. When data is captured, the user should consider if the data should be captured with either a relative accuracy or absolute accuracy, since this could not only influence how information will be interpreted but also the cost of data capture. After entering data into a GIS, the data usually requires editing, to remove errors, or further processing. For vector data it must be made "topologically correct" before it can be used for some advanced analysis. For example, in a road network, lines must connect with nodes at an intersection. Errors such as undershoots and overshoots must also be removed. For scanned maps, blemishes on the source map may need to be removed from the resulting
raster Raster may refer to: * Raster graphics, graphical techniques using arrays of pixel values * Raster graphics editor, a computer program * Raster scan, the pattern of image readout, transmission, storage, and reconstruction in television and computer ...
. For example, a fleck of dirt might connect two lines that should not be connected.


Projections, coordinate systems, and registration

The earth can be represented by various models, each of which may provide a different set of coordinates (e.g., latitude, longitude, elevation) for any given point on the Earth's surface. The simplest model is to assume the earth is a perfect sphere. As more measurements of the earth have accumulated, the models of the earth have become more sophisticated and more accurate. In fact, there are models called datums that apply to different areas of the earth to provide increased accuracy, like
North American Datum of 1983 The North American Datum (NAD) is the Geodetic datum#Horizontal datum, horizontal datum now used to define the Geodesy, geodetic network in North America. A datum is a formal description of the shape of the Earth along with an "anchor" point for ...
for U.S. measurements, and the
World Geodetic System The World Geodetic System (WGS) is a standard for use in cartography Cartography (; from χάρτης ''chartēs'', "papyrus, sheet of paper, map"; and γράφειν ''graphein'', "write") is the study and practice of making and using ...
for worldwide measurements. The latitude and longitude on a map made against a local datum may not be the same as one obtained from a
GPS receiver A satellite navigation device, colloquially called a GPS receiver, or simply a GPS, is a device that is capable of receiving information from GNSS satellites and then to calculate the device's geographical position. Using suitable software, the ...
. Converting coordinates from one datum to another requires a datum transformation such as a Helmert transformation, although in certain situations a simple
translation Translation is the communication of the meaning Meaning most commonly refers to: * Meaning (linguistics), meaning which is communicated through the use of language * Meaning (philosophy), definition, elements, and types of meaning discusse ...
may be sufficient. In popular GIS software, data projected in latitude/longitude is often represented as a
Geographic coordinate system A geographic coordinate system (GCS) is a coordinate system associated with positions on Earth (geographic position). A GCS can give positions: *as spherical coordinate system using latitude In geography, latitude is a geographic c ...
. For example, data in latitude/longitude if the datum is the 'North American Datum of 1983' is denoted by 'GCS North American 1983'.


Data quality

While no digital model can be a perfect representation of the real world, it is important that GIS data be of a high quality. In keeping with the principle of
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, the data must be close enough to reality so that the results of GIS procedures correctly correspond to the results of real world processes. This means that there is no single standard for data quality, because the necessary degree of quality depends on the scale and purpose of the tasks for which it is to be used. Several elements of data quality are important to GIS data: ; Accuracy :The degree of similarity between a represented measurement and the actual value; conversely, ''error'' is the amount of difference between them. In GIS data, there is concern for accuracy in representations of location (''positional accuracy''), property (''attribute accuracy''), and time. For example, the US 2020 Census says that the population of Houston on April 1 2020 was 2,304,580; if it was actually 2,310,674, this would be an error and thus a lack of attribute accuracy. ;Accuracy and precision , Precision :The degree of refinement in a represented value. In a quantitative property, this is the number of significant digits in the measured value. An imprecise value is vague or ambiguous, including a range of possible values. For example, if one were to say that the population of Houston on April 1 2020 was "about 2.3 million," this statement would be imprecise, but likely accurate because the correct value (and many incorrect values) are included. As with accuracy, representations of location, property, and time can all be more or less precise. ''Spatial resolution, Resolution'' is a commonly used expression of positional precision, especially in Raster graphics , raster data sets. ;Uncertainty :A general acknowledgement of the presence of error and imprecision in geographic data. That is, it is a degree of general doubt, given that it is difficult to know exactly how much error is present in a data set, although some form of estimate may be attempted (a confidence interval being such an estimate of uncertainty). This is sometimes used as a collective term for all or most aspects of data quality. ;Fuzzy concept , Vagueness or fuzziness :The degree to which an aspect (location, property, or time) of a phenomenon is inherently imprecise, rather than the imprecision being in a measured value. For example, the spatial extent of the Houston metropolitan area is vague, as there are places on the outskirts of the city that are less connected to the central city (measured by activities such as commuting) than places that are closer. Mathematical tools such as fuzzy set theory are commonly used to manage vagueness in geographic data. ;Completeness :The degree to which a data set represents all of the actual features that it purports to include. For example, if a layer of "roads in Houston" is missing some actual streets, it is incomplete. ;Currency :The most recent point in time at which a data set claims to be an accurate representation of reality. This is a concern for the majority of GIS applications, which attempt to represent the world "at present," in which case older data is of lower quality. ;Consistency :The degree to which the representations of the many phenomena in a data set correctly correspond with each other. Consistency in Geospatial topology, topological relationships between spatial objects is an especially important aspect of consistency. For example, if all of the lines in a street network were accidentally moved 10 meters to the East, they would be inaccurate but still consistent, because they would still properly connect at each intersection, and Transport network analysis , network analysis tools such as shortest path would still give correct results. ;Propagation of uncertainty :The degree to which the quality of the results of Spatial analysis methods and other processing tools derives from the quality of input data. For example, interpolation is a common operation used in many ways in GIS; because it generates estimates of values between known measurements, the results will always be more precise, but less certain (as each estimate has an unknown amount of error). GIS accuracy depends upon source data, and how it is encoded to be data referenced. Land surveyors have been able to provide a high level of positional accuracy utilizing the GPS-derived positions. High-resolution digital terrain and aerial imagery, powerful computers and Web technology are changing the quality, utility, and expectations of GIS to serve society on a grand scale, but nevertheless there are other source data that affect overall GIS accuracy like paper maps, though these may be of limited use in achieving the desired accuracy. In developing a digital topographic database for a GIS, topographical maps are the main source, and aerial photography and satellite imagery are extra sources for collecting data and identifying attributes which can be mapped in layers over a location facsimile of scale. The scale of a map and geographical rendering area representation type, or
map projection In cartography, a map projection is a way to flatten a globe's surface into a plane in order to make a map. This requires a systematic transformation of the latitudes and longitudes of locations from the Surface (mathematics), surface of the globe ...
, are very important aspects since the information content depends mainly on the scale set and resulting locatability of the map's representations. In order to digitize a map, the map has to be checked within theoretical dimensions, then scanned into a raster format, and resulting raster data has to be given a theoretical dimension by a rubber sheeting/warping technology process known as georeferencing. A quantitative analysis of maps brings accuracy issues into focus. The electronic and other equipment used to make measurements for GIS is far more precise than the machines of conventional map analysis. All geographical data are inherently inaccurate, and these inaccuracies will propagate through GIS operations in ways that are difficult to predict.


Raster-to-vector translation

Data restructuring can be performed by a GIS to convert data into different formats. For example, a GIS may be used to convert a satellite image map to a vector structure by generating lines around all cells with the same classification, while determining the cell spatial relationships, such as adjacency or inclusion. More advanced data processing can occur with image processing, a technique developed in the late 1960s by NASA and the private sector to provide contrast enhancement, false color rendering and a variety of other techniques including use of two dimensional Fourier transforms. Since digital data is collected and stored in various ways, the two data sources may not be entirely compatible. So a GIS must be able to convert geographic data from one structure to another. In so doing, the implicit assumptions behind different ontologies and classifications require analysis. Object ontologies have gained increasing prominence as a consequence of object-oriented programming and sustained work by Barry Smith (academic and ontologist), Barry Smith and co-workers.


Spatial ETL

Spatial ETL tools provide the data processing functionality of traditional extract, transform, load (ETL) software, but with a primary focus on the ability to manage spatial data. They provide GIS users with the ability to translate data between different standards and proprietary formats, whilst geometrically transforming the data en route. These tools can come in the form of add-ins to existing wider-purpose software such as spreadsheets.


Spatial analysis with GIS

GIS spatial analysis is a rapidly changing field, and GIS packages are increasingly including analytical tools as standard built-in facilities, as optional toolsets, as add-ins or 'analysts'. In many instances these are provided by the original software suppliers (commercial vendors or collaborative non commercial development teams), while in other cases facilities have been developed and are provided by third parties. Furthermore, many products offer software development kits (SDKs), programming languages and language support, scripting facilities and/or special interfaces for developing one's own analytical tools or variants. The increased availability has created a new dimension to business intelligence termed "Spatial intelligence (business method), spatial intelligence" which, when openly delivered via intranet, democratizes access to geographic and social network data. Geospatial intelligence, based on GIS spatial analysis, has also become a key element for security. GIS as a whole can be described as conversion to a vectorial representation or to any other digitisation process. Geoprocessing is a GIS operation used to manipulate spatial data. A typical geoprocessing operation takes an input dataset, performs an operation on that dataset, and returns the result of the operation as an output dataset. Common geoprocessing operations include geographic feature overlay, feature selection and analysis,
topology s, which have only one surface and one edge, are a kind of object studied in topology. In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structu ...

topology
processing, raster graphics, raster processing, and data conversion. Geoprocessing allows for definition, management, and analysis of information used to form decisions.


Terrain analysis

Many geographic tasks involve the terrain, the shape of the surface of the earth, such as hydrology, Earthworks (engineering), earthworks, and biogeography. Thus, terrain data is often a core dataset in a GIS, usually in the form of a raster Digital elevation model (DEM) or a Triangulated irregular network (TIN). A variety of tools are available in most GIS software for analyzing terrain, often by creating derivative datasets that represent a specific aspect of the surface. Some of the most common include: * Grade (slope), Slope or grade is the steepness or gradient of a unit of terrain, usually measured as an angle in degrees or as a percentage. * Aspect (geography), Aspect can be defined as the direction in which a unit of terrain faces. Aspect is usually expressed in degrees from north. * Cut and fill is a computation of the difference between the surface before and after an Earthworks (engineering), excavation project to estimate costs. * Hydrological modeling can provide a spatial element that other hydrological models lack, with the analysis of variables such as slope, aspect and watershed or Catchment area (human geography), catchment area. Terrain analysis is fundamental to hydrology, since water always flows down a slope. As basic terrain analysis of a digital elevation model (DEM) involves calculation of slope and aspect, DEMs are very useful for hydrological analysis. Slope and aspect can then be used to determine direction of surface runoff, and hence flow accumulation for the formation of streams, rivers and lakes. Areas of divergent flow can also give a clear indication of the boundaries of a catchment. Once a flow direction and accumulation matrix has been created, queries can be performed that show contributing or dispersal areas at a certain point. More detail can be added to the model, such as terrain roughness, vegetation types and soil types, which can influence infiltration and evapotranspiration rates, and hence influencing surface flow. One of the main uses of hydrological modeling is in GIS in environmental contamination, environmental contamination research. Other applications of hydrological modeling include GIS and hydrology, groundwater and surface water mapping, as well as flood risk maps. * Viewshed analysis predicts the impact that terrain has on the visibility between locations, which is especially important for wireless communications. * Shaded relief is a depiction of the surface as if it were a three dimensional model lit from a given direction, which is very commonly used in maps. Most of these are generated using algorithms that are discrete simplifications of vector calculus. Slope, aspect, and surface curvature in terrain analysis are all derived from neighborhood operations using elevation values of a cell's adjacent neighbours. Each of these is strongly affected by the level of detail in the terrain data, such as the resolution of a DEM, which should be chosen carefully.


Proximity analysis

Distance is a key part of solving many geographic tasks, usually due to the friction of distance. Thus, a wide variety of analysis tools have analyze distance in some form, such as Buffer analysis, buffers, Voronoi diagram , Voronoi or Thiessen polygons, Cost distance analysis, and Transport network analysis , network analysis.


Data analysis

It is difficult to relate wetlands maps to rainfall amounts recorded at different points such as airports, television stations, and schools. A GIS, however, can be used to depict two- and three-dimensional characteristics of the Earth's surface, subsurface, and atmosphere from information points. For example, a GIS can quickly generate a map with isopleth or contour lines that indicate differing amounts of rainfall. Such a map can be thought of as a rainfall contour map. Many sophisticated methods can estimate the characteristics of surfaces from a limited number of point measurements. A two-dimensional contour map created from the surface modeling of rainfall point measurements may be overlaid and analyzed with any other map in a GIS covering the same area. This GIS derived map can then provide additional information - such as the viability of water power potential as a renewable energy source. Similarly, GIS can be used to compare other renewable energy resources to find the best geographic potential for a region. Additionally, from a series of three-dimensional points, or digital elevation model, isopleth lines representing elevation contours can be generated, along with slope analysis, shaded relief, and other elevation products. Watersheds can be easily defined for any given reach, by computing all of the areas contiguous and uphill from any given point of interest. Similarly, an expected thalweg of where surface water would want to travel in intermittent and permanent streams can be computed from elevation data in the GIS.


Topological modeling

A GIS can recognize and analyze the spatial relationships that exist within digitally stored spatial data. These topological relationships allow complex spatial modelling and analysis to be performed. Topological relationships between geometric entities traditionally include adjacency (what adjoins what), containment (what encloses what), and proximity (how close something is to something else).


Geometric networks

Geometric networks are linear networks of objects that can be used to represent interconnected features, and to perform special spatial analysis on them. A geometric network is composed of edges, which are connected at junction points, similar to Graph (discrete mathematics), graphs in mathematics and computer science. Just like graphs, networks can have weight and flow assigned to its edges, which can be used to represent various interconnected features more accurately. Geometric networks are often used to model road networks and public utility networks, such as electric, gas, and water networks. Network modeling is also commonly employed in transportation planning, hydrology modeling, and infrastructure modeling.


Cartographic modeling

Dana Tomlin probably coined the term "cartographic modeling" in his PhD dissertation (1983); he later used it in the title of his book, ''Geographic Information Systems and Cartographic Modeling'' (1990). Cartographic modeling refers to a process where several thematic layer (disambiguation), layers of the same area are produced, processed, and analyzed. Tomlin used raster layers, but the overlay method (see below) can be used more generally. Operations on map layers can be combined into algorithms, and eventually into simulation or optimization models.


Map overlay

The combination of several spatial datasets (points, lines, or polygons) creates a new output vector dataset, visually similar to stacking several maps of the same region. These overlays are similar to mathematical Venn diagram overlays. A union (set theory), union overlay combines the geographic features and attribute tables of both inputs into a single new output. An intersection (set theory), intersect overlay defines the area where both inputs overlap and retains a set of attribute fields for each. A symmetric difference overlay defines an output area that includes the total area of both inputs except for the overlapping area. Data extraction is a GIS process similar to vector overlay, though it can be used in either vector or raster data analysis. Rather than combining the properties and features of both datasets, data extraction involves using a "clip" or "mask" to extract the features of one data set that fall within the spatial extent of another dataset. In raster data analysis, the overlay of datasets is accomplished through a process known as "local operation on multiple rasters" or "map algebra", through a function that combines the values of each raster's matrix (mathematics), matrix. This function may weigh some inputs more than others through use of an "index model" that reflects the influence of various factors upon a geographic phenomenon.


Geostatistics

Geostatistics is a branch of statistics that deals with field data, spatial data with a continuous index. It provides methods to model spatial correlation, and predict values at arbitrary locations (interpolation). When phenomena are measured, the observation methods dictate the accuracy of any subsequent analysis. Due to the nature of the data (e.g. traffic patterns in an urban environment; weather patterns over the Pacific Ocean), a constant or dynamic degree of precision is always lost in the measurement. This loss of precision is determined from the scale and distribution of the data collection. To determine the statistical relevance of the analysis, an average is determined so that points (gradients) outside of any immediate measurement can be included to determine their predicted behavior. This is due to the limitations of the applied statistic and data collection methods, and interpolation is required to predict the behavior of particles, points, and locations that are not directly measurable. Interpolation is the process by which a surface is created, usually a raster dataset, through the input of data collected at a number of sample points. There are several forms of interpolation, each which treats the data differently, depending on the properties of the data set. In comparing interpolation methods, the first consideration should be whether or not the source data will change (exact or approximate). Next is whether the method is subjective, a human interpretation, or objective. Then there is the nature of transitions between points: are they abrupt or gradual. Finally, there is whether a method is global (it uses the entire data set to form the model), or local where an algorithm is repeated for a small section of terrain. Interpolation is a justified measurement because of a spatial autocorrelation principle that recognizes that data collected at any position will have a great similarity to, or influence of those locations within its immediate vicinity. Digital elevation models, triangulated irregular networks, edge-finding algorithms, Thiessen polygons, Fourier analysis, Weighted moving average, (weighted) moving averages, inverse distance weighting, kriging, Spline (mathematics), spline, and Trend estimation, trend surface analysis are all mathematical methods to produce interpolative data.


Address geocoding

Geocoding is interpolating spatial locations (X,Y coordinates) from street addresses or any other spatially referenced data such as ZIP Codes, parcel lots and address locations. A reference theme is required to Geocoding, geocode individual addresses, such as a road centerline file with address ranges. The individual address locations have historically been interpolated, or estimated, by examining address ranges along a road segment. These are usually provided in the form of a table or database. The software will then place a dot approximately where that address belongs along the segment of centerline. For example, an address point of 500 will be at the midpoint of a line segment that starts with address 1 and ends with address 1,000. Geocoding can also be applied against actual parcel data, typically from municipal tax maps. In this case, the result of the geocoding will be an actually positioned space as opposed to an interpolated point. This approach is being increasingly used to provide more precise location information.


Reverse geocoding

Reverse geocoding is the process of returning an estimated street address number as it relates to a given coordinate. For example, a user can click on a road centerline theme (thus providing a coordinate) and have information returned that reflects the estimated house number. This house number is interpolated from a range assigned to that road segment. If the user clicks at the midpoint of a segment that starts with address 1 and ends with 100, the returned value will be somewhere near 50. Note that reverse geocoding does not return actual addresses, only estimates of what should be there based on the predetermined range.


Multi-criteria decision analysis

Coupled with GIS, multi-criteria decision analysis methods support decision-makers in analysing a set of alternative spatial solutions, such as the most likely ecological habitat for restoration, against multiple criteria, such as vegetation cover or roads. MCDA uses decision rules to aggregate the criteria, which allows the alternative solutions to be ranked or prioritised. GIS MCDA may reduce costs and time involved in identifying potential restoration sites.


GIS data mining

GIS or spatial data mining is the application of data mining methods to spatial data. Data mining, which is the partially automated search for hidden patterns in large databases, offers great potential benefits for applied GIS-based decision making. Typical applications include environmental monitoring. A characteristic of such applications is that spatial correlation between data measurements require the use of specialized algorithms for more efficient data analysis.


Data output and cartography

Cartography is the design and production of maps, or visual representations of spatial data. The vast majority of modern cartography is done with the help of computers, usually using GIS but production of quality cartography is also achieved by importing layers into a design program to refine it. Most GIS software gives the user substantial control over the appearance of the data. Cartographic work serves two major functions: First, it produces graphics on the screen or on paper that convey the results of analysis to the people who make decisions about resources. Wall maps and other graphics can be generated, allowing the viewer to visualize and thereby understand the results of analyses or simulations of potential events. Web Map Servers facilitate distribution of generated maps through web browsers using various implementations of web-based application programming interfaces (AJAX, Java programming, Java, Adobe Flash, Flash, etc.). Second, other database information can be generated for further analysis or use. An example would be a list of all addresses within one mile (1.6 km) of a toxic spill. An archeochrome is a new way of displaying spatial data. It is a thematic on a 3D map that is applied to a specific building or a part of a building. It is suited to the visual display of heat-loss data.


Terrain depiction

Traditional maps are abstractions of the real world, a sampling of important elements portrayed on a sheet of paper with symbols to represent physical objects. People who use maps must interpret these symbols. Topographic maps show the shape of land surface with contour lines or with Cartographic relief depiction, shaded relief. Today, graphic display techniques such as shading based on altitude in a GIS can make relationships among map elements visible, heightening one's ability to extract and analyze information. For example, two types of data were combined in a GIS to produce a perspective view of a portion of San Mateo County, California. *The digital elevation model, consisting of surface elevations recorded on a 30-meter horizontal grid, shows high elevations as white and low elevation as black. *The accompanying Landsat Thematic Mapper image shows a false-color infrared image looking down at the same area in 30-meter pixels, or picture elements, for the same coordinate points, pixel by pixel, as the elevation information. A GIS was used to register and combine the two images to Rendering (computer graphics), render the three-dimensional perspective view looking down the San Andreas Fault, using the Thematic Mapper image pixels, but shaded using the elevation of the landforms. The GIS display depends on the viewing point of the observation, observer and time of day of the display, to properly render the shadows created by the sun's rays at that latitude, longitude, and time of day.


Web mapping

In recent years there has been a proliferation of free-to-use and easily accessible mapping software such as the proprietary software, proprietary web applications Google Maps and Bing Maps, as well as the free and open-source software, free and open-source alternative OpenStreetMap. These services give the public access to huge amounts of geographic data, perceived by many users to be as trustworthy and usable as professional information. Some of them, like Google Maps and OpenLayers, expose an
application programming interface In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and so ...
(API) that enable users to create custom applications. These toolkits commonly offer street maps, aerial/satellite imagery, geocoding, searches, and routing functionality. Web mapping has also uncovered the potential of crowdsourcing geodata in projects like OpenStreetMap, which is a collaborative project to create a free editable map of the world. These Mashup (web application hybrid), mashup projects have been proven to provide a high level of value and benefit to end users outside that possible through traditional geographic information.


Applications

Since its origin in the 1960s, GIS has been used in an ever-increasing range of applications, corroborating the widespread importance of location and aided by the continuing reduction in the barriers to adopting geospatial technology. The perhaps hundreds of different uses of GIS can be classified in several ways: * ''Goal'': the purpose of an application can be broadly classified as either ''scientific research'' or ''resource management''. The purpose of research, defined as broadly as possible, is to discover new knowledge; this may be performed by someone who considers herself a scientist, but may also be done by anyone who is trying to learn why the world appears to work the way it does. A study as practical as deciphering why a business location has failed would be research in this sense. Management (sometimes called operational applications), also defined as broadly as possible, is the application of knowledge to make practical decisions on how to employ the resources one has control over to achieve one's goals. These resources could be time, capital, labor, equipment, land, mineral deposits, wildlife, and so on. ** ''Decision level'': Management applications have been further classified as ''strategic'', ''tactical'', ''operational'', a common classification in business management. Strategic tasks are long-term, visionary decisions about what goals one should have, such as whether a business should expand or not. Tactical tasks are medium-term decisions about how to achieve strategic goals, such as a national forest creating a grazing management plan. Operational decisions are concerned with the day-to-day tasks, such as a person finding the shortest route to a pizza restaurant. * ''Topic'': the domains in which GIS is applied largely fall into those concerned with human geography, the human world (e.g., Economic geography, economics, Political geography, politics, Transportation geography, transportation, education, landscape architecture, archaeology, urban planning, real estate, public health, crime mapping, defense (military), national defense), and those concerned with Physical geography, the natural world (e.g., Geological mapping, geology, Biogeography, biology, oceanography, Climatology, climate). That said, one of the powerful capabilities of GIS and the spatial perspective of geography is their integrative ability to compare disparate topics, and many applications are concerned with multiple domains. Examples of integrated human-natural application domains include Natural hazard mitigation, wildlife management, sustainable development, natural resources, and climate change response. * ''Institution'': GIS has been implemented in a variety of different kinds of institutions: ''government'' (at all levels from municipal to international), ''business'' (of all types and sizes), ''non-profit organizations'' (even churches), as well as ''personal'' uses. The latter has become increasingly prominent with the rise of location-enabled smartphones. * ''Lifespan'': GIS implementations may be focused on a ''project'' or an ''enterprise''. A Project GIS is focused on accomplishing a single task: data is gathered, analysis is performed, and results are produced separately from any other projects the person may perform, and the implementation is essentially transitory. An Enterprise GIS is intended to be a permanent institution, including a database that is carefully designed to be useful for a variety of projects over many years, and is likely used by many individuals across an enterprise, with some employed full-time just to maintain it. * ''Integration'': Traditionally, most GIS applications were ''standalone'', using specialized GIS software, specialized hardware, specialized data, and specialized professionals. Although these remain common to the present day, ''integrated'' applications have greatly increased, as geospatial technology was merged into broader enterprise applications, sharing IT infrastructure, databases, and software, often using enterprise integration platforms such as SAP. The implementation of a GIS is often driven by jurisdictional (such as a city), purpose, or application requirements. Generally, a GIS implementation may be custom-designed for an organization. Hence, a GIS deployment developed for an application, jurisdiction, enterprise, or purpose may not be necessarily Interoperability, interoperable or compatible with a GIS that has been developed for some other application, jurisdiction, enterprise, or purpose. GIS is also diverging into
location-based service A location-based service (LBS) is a general term denoting software services which use geographic data and information to provide services or information to users. LBS can be used in a variety of contexts, such as health, indoor object detection, ob ...
s, which allows GPS-enabled mobile devices to display their location in relation to fixed objects (nearest restaurant, gas station, fire hydrant) or mobile objects (friends, children, police car), or to relay their position back to a central server for display or other processing.


Open Geospatial Consortium standards

The Open Geospatial Consortium (OGC) is an international industry consortium of 384 companies, government agencies, universities, and individuals participating in a consensus process to develop publicly available geoprocessing specifications. Open interfaces and protocols defined by OpenGIS Specifications support interoperable solutions that "geo-enable" the Web, wireless and location-based services, and mainstream IT, and empower technology developers to make complex spatial information and services accessible and useful with all kinds of applications. Open Geospatial Consortium protocols include Web Map Service, and Web Feature Service. GIS products are broken down by the OGC into two categories, based on how completely and accurately the software follows the OGC specifications. ''Compliant products'' are software products that comply to OGC's OpenGIS Specifications. When a product has been tested and certified as compliant through the OGC Testing Program, the product is automatically registered as "compliant" on this site. ''Implementing products'' are software products that implement OpenGIS Specifications but have not yet passed a compliance test. Compliance tests are not available for all specifications. Developers can register their products as implementing draft or approved specifications, though OGC reserves the right to review and verify each entry.


Adding the dimension of time

The condition of the Earth's surface, atmosphere, and subsurface can be examined by feeding satellite data into a GIS. GIS technology gives researchers the ability to examine the variations in Earth processes over days, months, and years. As an example, the changes in vegetation vigor through a growing season can be animated to determine when drought was most extensive in a particular region. The resulting graphic represents a rough measure of plant health. Working with two variables over time would then allow researchers to detect regional differences in the lag between a decline in rainfall and its effect on vegetation. GIS technology and the availability of digital data on regional and global scales enable such analyses. The satellite sensor output used to generate a vegetation graphic is produced for example by the advanced very-high-resolution radiometer (AVHRR). This sensor system detects the amounts of energy reflected from the Earth's surface across various bands of the spectrum for surface areas of about 1 square kilometer. The satellite sensor produces images of a particular location on the Earth twice a day. AVHRR and more recently the moderate-resolution imaging spectroradiometer (MODIS) are only two of many sensor systems used for Earth surface analysis. In addition to the integration of time in environmental studies, GIS is also being explored for its ability to track and model the progress of humans throughout their daily routines. A concrete example of progress in this area is the recent release of time-specific population data by the U.S. Census. In this data set, the populations of cities are shown for daytime and evening hours highlighting the pattern of concentration and dispersion generated by North American commuting patterns. The manipulation and generation of data required to produce this data would not have been possible without GIS. Using models to project the data held by a GIS forward in time have enabled planners to test policy decisions using spatial decision support systems.


Semantics

Tools and technologies emerging from the World Wide Web Consortium's Semantic Web are proving useful for data integration problems in information systems. Correspondingly, such technologies have been proposed as a means to facilitate interoperability and data reuse among GIS applications. and also to enable new analysis mechanisms. Ontology (computer science), Ontologies are a key component of this semantic approach as they allow a formal, machine-readable specification of the concepts and relationships in a given domain. This in turn allows a GIS to focus on the intended meaning of data rather than its syntax or structure. For example, reasoning that a land cover type classified as ''deciduous needleleaf trees'' in one dataset is a specialization or subset of land cover type ''forest'' in another more roughly classified dataset can help a GIS automatically merge the two datasets under the more general land cover classification. Tentative ontologies have been developed in areas related to GIS applications, for example the hydrology ontology developed by the Ordnance Survey in the United Kingdom and the SWEET ontologies developed by NASA's Jet Propulsion Laboratory. Also, simpler ontologies and semantic metadata standards are being proposed by the W3C Geo Incubator Group to represent geospatial data on the web. GeoSPARQL is a standard developed by the Ordnance Survey, United States Geological Survey, Natural Resources Canada, Australia's Commonwealth Scientific and Industrial Research Organisation and others to support ontology creation and reasoning using well-understood OGC literals (GML, WKT), topological relationships (Simple Features, RCC8, DE-9IM), RDF and the SPARQL database query protocols. Recent research results in this area can be seen in the International Conference on Geospatial Semantics and the Terra Cognita – Directions to the Geospatial Semantic Web workshop at the International Semantic Web Conference.


Implications of GIS on society

With the popularization of GIS in decision making, scholars have begun to scrutinize the social and political implications of GIS. GIS can also be misused to distort reality for individual and political gain. It has been argued that the production, distribution, utilization, and representation of geographic information are largely related with the social context and has the potential to increase citizen trust in government. Other related topics include discussion on copyright, privacy, and censorship. A more optimistic social approach to GIS adoption is to use it as a tool for public participation.


In education

At the end of the 20th century, GIS began to be recognized as tools that could be used in the classroom. The benefits of GIS in education seem focused on developing spatial thinking, but there is not enough bibliography or statistical data to show the concrete scope of the use of GIS in education around the world, although the expansion has been faster in those countries where the curriculum mentions them. GIS seem to provide many advantages in teaching geography because they allow for analyses based on real geographic data and also help raise many research questions from teachers and students in classrooms. They also contribute to improvement in learning by developing spatial and geographical thinking and, in many cases, student motivation.


In local government

GIS is proven as an organization-wide, enterprise and enduring technology that continues to change how local government operates. Government agencies have adopted GIS technology as a method to better manage the following areas of government organization: * Economic development departments use interactive GIS mapping tools, aggregated with other data (demographics, labor force, business, industry, talent) along with a database of available commercial sites and buildings in order to attract investment and support existing business. Businesses making location decisions can use the tools to choose communities and sites that best match their criteria for success. * Public safety operations such as emergency operations centers, fire prevention, police and sheriff mobile technology and dispatch, and mapping weather risks. * Parks and recreation departments and their functions in asset inventory, land conservation, land management, and cemetery management * Public works and utilities, tracking water and stormwater drainage, electrical assets, engineering projects, and public transportation assets and trends * Fiber network management for interdepartmental network assets * School analytical and demographic data, asset management, and improvement/expansion planning * Public administration for election data, property records, and zoning/management The Open Data initiative is pushing local government to take advantage of technology such as GIS technology, as it encompasses the requirements to fit the Open Data/Open Government model of transparency. With Open Data, local government organizations can implement Citizen Engagement applications and online portals, allowing citizens to see land information, report potholes and signage issues, view and sort parks by assets, view real-time crime rates and utility repairs, and much more. The push for open data within government organizations is driving the growth in local government GIS technology spending, and database management.


See also

* AM/FM/GIS *
ArcGIS ArcGIS is a geographic information system (GIS) for working with maps and geographic information maintained by the Esri, Environmental Systems Research Institute (Esri). It is used for creating and using maps, compiling geographic data, analyzing m ...
* At-location mapping * Automotive navigation system * Cadastral map * Collaborative mapping * Comparison of GIS software * Counter-mapping * CyberGIS * Digital geologic mapping * Distributed GIS * Geographic information systems in China * Geographic information systems in geospatial intelligence * Geoinformatics * Geomatics * GIS and aquatic science * GIS and public health * GISCorps * GIS Day * GIS in archaeology * GvSIG * Historical GIS * Integrated Geo Systems * List of GIS data sources * List of GIS software * Map database management * Participatory GIS *
QGIS QGIS (until 2013 known as Quantum GIS) is a free and open-source cross-platform In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of al ...
* SAGA GIS * TerrSet * Traditional knowledge GIS * Virtual globe


References


Further reading

* Berry, J. K. (1993). ''Beyond Mapping: Concepts, Algorithms and Issues in GIS''. Fort Collins, CO: GIS World Books. * Bolstad, P. (2019). ''GIS Fundamentals: A first text on Geographic Information Systems, Sixth Edition''. Ann Arbor: XanEdu, 764 pp. * Burrough, P. A. and McDonnell, R. A. (1998). ''Principles of geographical information systems''. Oxford University Press, Oxford, 327 pp. * * Chang, K. (2007). ''Introduction to Geographic Information System, 4th Edition''. McGraw Hill, * * Elangovan, K. (2006). "GIS: Fundamentals, Applications and Implementations", New India Publishing Agency, New Delhi" 208 pp. * Fu, P., and J. Sun (2010). ''Web GIS: Principles and Applications''. ESRI Press. Redlands, CA. . * Harvey, Francis (2008). ''A Primer of GIS, Fundamental geographic and cartographic concepts.'' The Guilford Press, 31 pp. * Heywood, I., Cornelius, S., and Carver, S. (2006). ''An Introduction to Geographical Information Systems''. Prentice Hall. 3rd edition. * Paul Longley, Longley, P.A., Michael Frank Goodchild, Goodchild, M.F., Maguire, D.J. and David William Rhind, Rhind, D.W. (2005). ''Geographic Information Systems and Science''. Chichester: Wiley. 2nd edition. * Maguire, D.J., Goodchild M.F., Rhind D.W. (1997). "Geographic Information Systems: principles, and applications" Longman Scientific and Technical, Harlow. * * * Ott, T. and Swiaczny, F. (2001) .''Time-integrative GIS. Management and analysis of spatio-temporal data'', Berlin / Heidelberg / New York: Springer. * Pickles, J., ed., (1994) ''Ground Truth: The Social Implications of Geographic Information Systems'', New York and London: Guilford, 248 pp. * * * Thurston, J., Poiker, T.K. and J. Patrick Moore. (2003). ''Integrated Geospatial Technologies: A Guide to GPS, GIS, and Data Logging''. Hoboken, New Jersey: Wiley. * * * Wheatley, David and Gillings, Mark (2002). ''Spatial Technology and Archaeology. The Archaeological Application of GIS''. London, New York, Taylor & Francis. *


External links

* {{DEFAULTSORT:Geographic Information System Geographic information systems,