A spatial reference system (SRS) or coordinate reference system (CRS) is a framework used to precisely measure locations on the surface of the Earth as coordinates. It is thus the application of the abstract mathematics of

coordinate system In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine the position of the points or other geometric elements on a manifold such as Euclidean space. The order of the coordinates is sig ...

s and

analytic geometry In classical mathematics, analytic geometry, also known as coordinate geometry or Cartesian geometry, is the study of geometry using a coordinate system. This contrasts with synthetic geometry. Analytic geometry is used in physics and enginee ...

to geographic space. A particular SRS specification (for example, "

Universal Transverse Mercator The Universal Transverse Mercator (UTM) is a map projection system for assigning coordinates to locations on the surface of the Earth. Like the traditional method of latitude and longitude, it is a horizontal position representation, which means i ...

WGS 84 The World Geodetic System (WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS. The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also descri ...

Zone 16N") comprises a choice of

Earth ellipsoid An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximations ...

, horizontal datum,

map projection In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and l ...

(except in the

geographic coordinate system The geographic coordinate system (GCS) is a spherical or ellipsoidal coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various ...

), origin point, and unit of measure. Thousands of coordinate systems have been specified for use around the world or in specific regions and for various purposes, necessitating transformations between different SRS. Although they date to the Hellenic Period, spatial reference systems are now a crucial basis for the sciences and technologies of

Geoinformatics Geoinformatics is the science and the technology which develops and uses information science infrastructure to address the problems of geography, cartography, geosciences and related branches of science and engineering, such as Land Surveying. ...

, including

cartography Cartography (; from grc, χάρτης , "papyrus, sheet of paper, map"; and , "write") is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an i ...

geographic information systems A geographic information system (GIS) is a type of database containing geographic data (that is, descriptions of phenomena for which location is relevant), combined with software tools for managing, analyzing, and visualizing those data. In a ...

surveying Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ...

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 or on-site observation. The term is applied especially to acquiring information about Ear ...

, and

civil engineering Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewa ...

. This has led to their standardization in international specifications such as the EPSG codes and ''ISO 19111:2007 Geographic information—Spatial referencing by coordinates'', prepared by

ISO/TC 211 ISO/TC 211 is a standard technical committee formed within ISO, tasked with covering the areas of digital geographic information (such as used by geographic information systems) and geomatics. It is responsible for preparation of a series of Inte ...

, also published by the

Open Geospatial Consortium The Open Geospatial Consortium (OGC), an international voluntary consensus standards organization for geospatial content and location-based services, sensor web and Internet of Things, GIS data processing and data sharing. It originated in 199 ...

as ''Abstract Specification, Topic 2: Spatial referencing by coordinate''.

Types of systems

The thousands of spatial reference systems used today are based on a few general strategies, which have been defined in the EPSG, ISO, and OGC standards: ;

Geographic coordinate system The geographic coordinate system (GCS) is a spherical or ellipsoidal coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various ...

(or geodetic) :A

spherical coordinate system In mathematics, a spherical coordinate system is a coordinate system for three-dimensional space where the position of a point is specified by three numbers: the ''radial distance'' of that point from a fixed origin, its ''polar angle'' measu ...

measuring locations directly on the Earth (modeled as a

sphere A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the c ...

or ellipsoid) using

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...

(degrees north or south of the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also ...

) and

longitude Longitude (, ) is a geographic coordinate that specifies the east– west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek let ...

(degrees west or east of a

prime meridian A prime meridian is an arbitrary meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian (the 180th meridian in a 360°-system) form a great ...

). ; Geocentric coordinate system (or Earth-centered Earth-fixed) :A three-dimensional

cartesian coordinate system A Cartesian coordinate system (, ) in a plane is a coordinate system that specifies each point uniquely by a pair of numerical coordinates, which are the signed distances to the point from two fixed perpendicular oriented lines, measured in ...

that models the Earth as a three-dimensional object, measuring locations from a center point, usually the

center of mass In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...

of the Earth, along x, y, and z axes aligned with the

and the

. This system is commonly used to track the orbits of

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...

s, because they are based on the center of mass. Thus, this is the internal coordinate system used by

Satellite navigation A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location ( longitude, latitude, and altitude/ elevation) to hig ...

systems such as GPS to compute locations using

multilateration Trilateration is the use of distances (or "ranges") for determining the unknown position coordinates of a point of interest, often around Earth (geopositioning). When more than three distances are involved, it may be called multilateration, for e ...

. ; Projected coordinate system (or planar, grid) Utm-latlon grid en

:A standardized

that models the Earth (or more commonly, a large region thereof) as a plane, measuring locations from an arbitrary origin point along x and y axes more or less aligned with the cardinal directions. Each of these systems is based on a particular

Map projection In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and l ...

to create a planar surface from the curved Earth surface. These are generally defined and used strategically to minimize the distortions inherent to projections. Common examples include the

Universal transverse mercator The Universal Transverse Mercator (UTM) is a map projection system for assigning coordinates to locations on the surface of the Earth. Like the traditional method of latitude and longitude, it is a horizontal position representation, which means i ...

(UTM) and national systems such as the British National Grid, and

State Plane Coordinate System The State Plane Coordinate System (SPCS) is a set of 124 geographic zones or coordinate systems designed for specific regions of the United States. Each state contains one or more state plane zones, the boundaries of which usually follow county li ...

(SPCS). ;Engineering coordinate system (or local, custom) :A

(2-D or 3-D) that is created bespoke for a small area, often a single engineering project, over which the curvature of the Earth can be safely approximated as flat without significant distortion. Locations are typically measured directly from an arbitrary origin point using

techniques. These may or may not be aligned with a standard projected coordinate system.

Local tangent plane coordinates Local tangent plane coordinates (LTP), also known as local ellipsoidal system, local geodetic coordinate system, or local vertical, local horizontal coordinates (LVLH), are a spatial reference system based on the tangent plane defined by the local ...

are a type of local coordinate system used in aviation and marine vehicles. These standards acknowledge that standard reference systems also exist for measuring

elevation The elevation of a geographic 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 surface (see Geodetic datum § ...

using

vertical datum In geodesy, surveying, hydrography and navigation, vertical datum or altimetric datum, is a reference coordinate surface used for vertical positions, such as the elevations of Earth-bound features (terrain, bathymetry, water level, and built str ...

s and time (e.g.

ISO 8601 ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the Geneva-based International Organization for Standardization (ISO) and was first published in 1988, w ...

), which may be combined with a spatial reference system to form a ''compound coordinate system'' for representing three-dimensional and/or spatio-temporal locations. There are also internal systems for measuring location within the context of an object, such as the rows and columns of pixels in a raster image, Linear referencing measurements along linear features (e.g., highway mileposts), and systems for specifying location within moving objects such as ships. The latter two are often classified as subcategories of engineering coordinate systems.

Components

The goal of any spatial reference system is to create a common reference frame in which locations can be measured precisely and consistently as coordinates, which can then be shared unambiguously, so that any recipient can identify the same location that was originally intended by the originator. To accomplish this, any coordinate reference system definition needs to be composed of several specifications: * A

, an abstract framework for measuring locations. Like any mathematical coordinate system, its definition consists of a measurable space (whether a plane, a three-dimension void, or the surface of an object such as the Earth), an origin point, a set of axis vectors emanating from the origin, and a unit of measure. * A horizontal datum, which binds the abstract coordinate system to the real space of the Earth. A horizontal datum can be defined as a precise reference framework for measuring geographic coordinates (latitude and longitude). Examples include the

World Geodetic System The World Geodetic System (WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS. The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also descr ...

and the 1927 and 1983

North American Datum The North American Datum (NAD) is the horizontal datum now used to define the geodetic network in North America. A datum is a formal description of the shape of the Earth along with an "anchor" point for the coordinate system. In surveying, ...

. A datum generally consists of an estimate of the shape of the Earth (usually an ellipsoid), and one or more ''anchor points'' or ''control points'', established locations (often marked by physical monuments) for which the measurement is documented. * A definition for a projected CRS must also a choice of

to convert the spherical coordinates specified by the datum into cartesian coordinates on a planar surface. Thus, a CRS definition will typically consist of a "stack" of dependent specifications, as exemplified in the following table:

Examples by continent

Examples of systems around the world are:

Asia

* Chinese Global Navigation Grid Code, China * Israeli Cassini Soldner, Israel *

Israeli Transverse Mercator Israeli Transverse Mercator (ITM), also known as the New Israel Grid (NIG; he, רשת ישראל חדשה, רשת ישראל החדשה ''Reshet Yisra'el Ha-Ḥadasha'') is the new geographic coordinate system for Israel. The name is derived f ...

, Israel * Jordan Transverse Mercator, Jordan

Europe

British national grid reference system The Ordnance Survey National Grid reference system (OSGB) (also known as British National Grid (BNG)) is a system of geographic grid references used in Great Britain, distinct from latitude and longitude. The Ordnance Survey (OS) devised the ...

, Britain * Lambert-93 (fr), the official projection in

Metropolitan France Metropolitan France (french: France métropolitaine or ''la Métropole''), also known as European France (french: Territoire européen de la France) is the area of France which is geographically in Europe. This collective name for the European ...

Hellenic Geodetic Reference System 1987 The Hellenic Geodetic Reference System 1987 or HGRS87 ( el, Ελληνικό Γεωδετικό Σύστημα Αναφοράς 1987 or ΕΓΣΑ'87) is a geodetic system commonly used in Greece ( SRID=2100). The system specifies a local geodetic da ...

, Greece *

Irish grid reference system The Irish grid reference system is a system of geographic grid references used for paper mapping in Ireland (both Northern Ireland and the Republic of Ireland). The Irish grid partially overlaps the British grid, and uses a similar co-ordinat ...

, Ireland *

Irish Transverse Mercator Irish Transverse Mercator (ITM) is the geographic coordinate system for Ireland. It was implemented jointly by the Ordnance Survey Ireland (OSi) and the Ordnance Survey of Northern Ireland (OSNI) in 2001. The name is derived from the Transve ...

, Ireland * SWEREF 99 (sv), Sweden

North America

* United States National Grid, US

Worldwide

Universal Transverse Mercator coordinate system The Universal Transverse Mercator (UTM) is a map projection system for assigning coordinates to locations on the surface of the Earth. Like the traditional method of latitude and longitude, it is a horizontal position representation, which means i ...

Lambert conformal conic projection A Lambert conformal conic projection (LCC) is a conic map projection used for aeronautical charts, portions of the State Plane Coordinate System, and many national and regional mapping systems. It is one of seven projections introduced by Jo ...

* International mapcode system *

Military Grid Reference System The Military Grid Reference System (MGRS)
Datums, Ellipsoids, Grids, and Grid Reference Sys ...

Identifiers

A Spatial Reference System Identifier (SRID) is a unique value used to unambiguously identify projected, unprojected, and local spatial coordinate system definitions. These coordinate systems form the heart of all GIS applications. Virtually all major spatial vendors have created their own SRID implementation or refer to those of an authority, such as the

EPSG Geodetic Parameter Dataset EPSG Geodetic Parameter Dataset (also EPSG registry) is a public registry of geodetic datums, spatial reference systems, Earth ellipsoids, coordinate transformations and related units of measurement. Originally created by European Petroleum Surv ...

. SRIDs are the primary key for the Open Geospatial Consortium (OGC) spatial_ref_sys metadata table for the Simple Features for SQL Specification, Versions 1.1 and 1.2, which is defined as follows: CREATE TABLE SPATIAL_REF_SYS ( SRID INTEGER NOT NULL PRIMARY KEY, AUTH_NAME CHARACTER VARYING(256), AUTH_SRID INTEGER, SRTEXT CHARACTER VARYING(2048) ) In spatially enabled databases (such as

IBM Db2 Db2 is a family of data management products, including database servers, developed by IBM. It initially supported the relational model, but was extended to support object–relational features and non-relational structures like JSON a ...

IBM Informix IBM Informix is a product family within IBM's Information Management division that is centered on several relational database management system (RDBMS) offerings. The Informix products were originally developed by Informix Corporation, whose ...

Ingres Jean-Auguste-Dominique Ingres ( , ; 29 August 1780 – 14 January 1867) was a French Neoclassical painter. Ingres was profoundly influenced by past artistic traditions and aspired to become the guardian of academic orthodoxy against the a ...

Microsoft SQL Server Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which ...

, MonetDB,

MySQL MySQL () is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A relational database ...

Oracle RDBMS Oracle Database (commonly referred to as Oracle DBMS, Oracle Autonomous Database, or simply as Oracle) is a multi-model database management system produced and marketed by Oracle Corporation. It is a database commonly used for running online ...

Teradata Teradata Corporation is an American software company that provides cloud database and analytics-related software, products, and services. The company was formed in 1979 in Brentwood, California, as a collaboration between researchers at Caltech ...

PostGIS PostGIS ( ) is an open source software program that adds support for geographic objects to the PostgreSQL object-relational database. PostGIS follows the Simple Features for SQL specification from the Open Geospatial Consortium (OGC). Technica ...

, SQL Anywhere and

Vertica Vertica Systems is an analytic database management software company. Vertica was founded in 2005 by the database researcher Michael Stonebraker, with Andrew Palmer as the founding CEO. Ralph Breslauer and Christopher P. Lynch served as later ...

), SRIDs are used to uniquely identify the coordinate systems used to define columns of spatial data or individual spatial objects in a spatial column (depending on the spatial implementation). SRIDs are typically associated with a

well-known text Well-known text (WKT) is a text markup language for representing vector geometry objects. A binary equivalent, known as well-known binary (WKB), is used to transfer and store the same information in a more compact form convenient for computer pr ...

(WKT) string definition of the coordinate system (SRTEXT, above). Here are two common coordinate systems with their EPSG SRID value followed by their WKT: UTM, Zone 17N, NAD27 — SRID 2029: PROJCS["NAD27(76) / UTM zone 17N", GEOGCS["NAD27(76)", DATUM["North_American_Datum_1927_1976", SPHEROID["Clarke 1866",6378206.4,294.9786982138982, AUTHORITY["EPSG","7008", AUTHORITY["EPSG","6608", PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901", UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122", AUTHORITY EPSG","4608", UNIT metre",1, ________AUTHORITY["EPSG","9001", ____PROJECTION["Transverse_Mercator".html" ;"title="EPSG","9001".html" ;"title="metre",1, AUTHORITY["EPSG","9001"">metre",1, AUTHORITY["EPSG","9001", PROJECTION["Transverse_Mercator"">EPSG","9001".html" ;"title="metre",1, AUTHORITY["EPSG","9001"">metre",1, AUTHORITY["EPSG","9001", PROJECTION["Transverse_Mercator" PARAMETER["latitude_of_origin",0], PARAMETER["central_meridian",-81], PARAMETER["scale_factor",0.9996], PARAMETER["false_easting",500000], PARAMETER["false_northing",0], AUTHORITY["EPSG","2029"], AXIS["Easting",EAST], AXIS Northing",NORTH

WGS84 The World Geodetic System (WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS. The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also desc ...

— SRID 4326 GEOGCS WGS 84", DATUM["WGS_1984", SPHEROID["WGS 84",6378137,298.257223563, AUTHORITY["EPSG","7030", AUTHORITY["EPSG","6326", PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901", UNIT["degree",0.01745329251994328, AUTHORITY["EPSG","9122", AUTHORITY["EPSG","4326" SRID values associated with spatial data can be used to constrain spatial operations — for instance, spatial operations cannot be performed between spatial objects with differing SRIDs in some systems, or trigger coordinate system transformations between spatial objects in others.

References

External links

spatialreference.org
– A website that defines spatial reference systems, in a variety of formats.
OpenGIS Specifications (Standards)

OpenGIS Simple Features Specification for CORBA (99-054)

OpenGIS Simple Features Specification for OLE/COM (99-050)

OpenGIS Simple Features Specification for SQL (99-054, 05-134, 06-104r3)

OGR
— library implementing relevant OGC standards
EPSG Geodetic Parameter Registry
- search engine for EPSG defined reference systems
EPSG.io/
- Full text search indexing over 6000 coordinate systems
Galdos Systems INdicio CRS Registry
{{DEFAULTSORT:Spatial Referencing System Geographic coordinate systems Geographic information systems Geodesy ISO/TC 211 Open Geospatial Consortium GIS file formats