A spatial reference system (SRS) or coordinate reference system (CRS) is a framework used to precisely measure locations on the surface of 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 and standardize the position of the points or other geometric elements on a manifold such as Euclidean space. The coordinates are ...

s and

analytic geometry In 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 engineering, and als ...

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 mean ...

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 approximation ...

, horizontal datum,

map projection In cartography, a map projection is any of a broad set of Transformation (function) , transformations employed to represent the curved two-dimensional Surface (mathematics), surface of a globe on a Plane (mathematics), plane. In a map projection, ...

(except in the

geographic coordinate system A geographic coordinate system (GCS) is a spherical coordinate system, spherical or geodetic coordinates, geodetic coordinate system for measuring and communicating position (geometry), positions directly on Earth as latitude and longitude. ...

), 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

Hellenistic period In classical antiquity, the Hellenistic period covers the time in Greek history after Classical Greece, between the death of Alexander the Great in 323 BC and the death of Cleopatra VII in 30 BC, which was followed by the ascendancy of the R ...

, spatial reference systems are now a crucial basis for the sciences and technologies of

Geoinformatics Geoinformatics is a scientific field primarily within the domains of Computer Science and technical geography. It focuses on the programming of applications, spatial data structures, and the analysis of objects and space-time phenomena relate ...

, including

cartography Cartography (; from , '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 imagined reality) can ...

geographic information systems A geographic information system (GIS) consists of integrated computer hardware and software that store, manage, analyze, edit, output, and visualize geographic data. Much of this often happens within a spatial database; however, this is not ...

surveying Surveying or land surveying is the technique, profession, art, and science of determining the land, terrestrial Plane (mathematics), two-dimensional or Three-dimensional space#In Euclidean geometry, three-dimensional positions of Point (geom ...

remote sensing Remote sensing is the acquisition of information about an physical object, 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 inform ...

, and

civil engineering Civil engineering is a regulation and licensure in engineering, professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads ...

. This has led to their standardization in international specifications such as the

EPSG code EPSG Geodetic Parameter Dataset (also EPSG registry) is a public registry of Geodetic datum, geodetic datums, Spatial reference system, spatial reference systems, Earth ellipsoid, Earth ellipsoids, coordinate transformations and related Unit of me ...

s and ''ISO 19111:2019 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 I ...

, also published by the

Open Geospatial Consortium The Open Geospatial Consortium (OGC) is an international voluntary consensus standards organization that develops and maintains international standards for geospatial content and location-based services, sensor web, Internet of Things, Geographi ...

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 A geographic coordinate system (GCS) is a spherical coordinate system, spherical or geodetic coordinates, geodetic coordinate system for measuring and communicating position (geometry), positions directly on Earth as latitude and longitude. ...

(or geodetic) :A

spherical coordinate system In mathematics, a spherical coordinate system specifies a given point in three-dimensional space by using a distance and two angles as its three coordinates. These are * the radial distance along the line connecting the point to a fixed point ...

measuring locations directly on the Earth (modeled as a

sphere A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...

ellipsoid An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional Scaling (geometry), scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a Surface (mathemat ...

) using

latitude In geography, latitude is a geographic coordinate system, geographic 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 t ...

(degrees north or south of the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

) 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 lett ...

(degrees west or east of a

prime meridian A prime meridian is an arbitrarily chosen meridian (geography), meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. On a spheroid, a prime meridian and its anti-meridian (the 180th meridian ...

). ;

Geocentric coordinate system The Earth-centered, Earth-fixed coordinate system (acronym ECEF), also known as the geocentric coordinate system, is a cartesian spatial reference system that represents locations in the vicinity of the Earth (including its surface, interior ...

(or Earth-centered Earth-fixed) :A three-dimensional

cartesian coordinate system In geometry, a Cartesian coordinate system (, ) in a plane (geometry), plane is a coordinate system that specifies each point (geometry), point uniquely by a pair of real numbers called ''coordinates'', which are the positive and negative number ...

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 barycenter or balance point) is the unique point at any given time where the weight function, weighted relative position (vector), position of the d ...

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 an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

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 geopositioning. A satellite navigation system with global coverage is termed global navigation satellite system (GNSS). , four global systems are ope ...

systems such as

GPS The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide geol ...

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, f ...

. ; 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, a map projection is any of a broad set of Transformation (function) , transformations employed to represent the curved two-dimensional Surface (mathematics), surface of a globe on a Plane (mathematics), plane. In a map projection, ...

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 mean ...

(UTM) and national systems such as the

British National Grid The Ordnance Survey National Grid reference system (OSGB), also known as British National Grid (BNG), is a system of geographic grid references, distinct from latitude and longitude, whereby any location in Great Britain can be described in te ...

, and State Plane Coordinate System (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) are part of a spatial reference system based on the tangent plane defined by the local vertical direction and the Earth's axis of rotation. They are also known as local ellipsoidal system, local geodetic coo ...

are a type of local coordinate system used in aviation and marine vehicles. ;Vertical reference frame: a standard reference system for measuring

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 equipotenti ...

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 stru ...

s, based on

levelling Levelling or leveling (American English; see spelling differences) is a branch of surveying, the object of which is to establish or verify or measure the height of specified points relative to a datum. It is widely used in geodesy and cartogra ...

, a

geoid The geoid ( ) is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is exte ...

model, or a

chart datum A chart datum is the water surface serving as origin (or coordinate surface) of depths displayed on a nautical chart and for reporting and predicting tide heights. A chart datum is generally derived from some tidal phase, in which case it is ...

(considering

tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

). These standards acknowledge that standard reference systems also exist for

time Time is the continuous progression of existence that occurs in an apparently irreversible process, irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequ ...

(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 International Organization for Standardization (ISO) and was first published in 1988, with updates in ...

). These 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 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 combination of the values for ...

Linear referencing Linear referencing, also called linear reference system or linear referencing system (LRS), is a method of spatial referencing over linear or curvilinear elements, such as roads or rivers. In LRS, the locations of physical features are described ...

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

geodetic datum A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame, or terrestrial reference frame) is a global datum reference or reference frame for unambiguously representing the positi ...

(horizontal, vertical, or three-dimensional) 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 A geographic coordinate system (GCS) is a spherical or geodetic coordinate system for measuring and communicating positions directly on Earth as latitude and longitude. It is the simplest, oldest, and most widely used type of the various ...

(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 describ ...

and the 1927 and 1983

North American Datum 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 fo ...

. 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 include 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; ''Reshet Yisra'el Ha-Ḥadasha'') is the new geographic coordinate system for Israel. The name is derived from the transverse Mercator projection it uses and the fact t ...

, 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, distinct from latitude and longitude, whereby any location in Great Britain can be described in ...

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

Metropolitan France Metropolitan France ( or ), also known as European France (), is the area of France which is geographically in Europe and chiefly comprises #Hexagon, the mainland, popularly known as "the Hexagon" ( or ), and Corsica. This collective name for the ...

* Hellenic Geodetic Reference System 1987, 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). Any location in Ireland can be described in terms of its distance from the origin ( ...

, 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 Transver ...

, 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 Geographic coordinate system, coordinates to locations on the surface of the Earth. Like the traditional method of latitude and longitude, it is a horizontal positi ...

* Lambert conformal conic projection * International mapcode system *

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

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 A geographic information system (GIS) consists of integrated computer hardware and software that store, manage, analyze, edit, output, and visualize geographic data. Much of this often happens within a spatial database; however, this is not ...

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, originated by a member of the European Petro ...

. 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,

IBM Informix Informix is a product family within IBM's Information Management division that is centered on several relational database management system (RDBMS) and multi-model database offerings. The Informix products were originally developed by Infor ...

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

Microsoft SQL Server Microsoft SQL Server is a proprietary relational database management system developed by Microsoft using Structured Query Language (SQL, often pronounced "sequel"). As a database server, it is a software product with the primary function of ...

MonetDB MonetDB is an open-source column-oriented relational database management system (RDBMS) originally developed at the Centrum Wiskunde & Informatica (CWI) in the Netherlands. It is designed to provide high performance on complex queries against l ...

MySQL MySQL () is an Open-source software, 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 rel ...

, Oracle RDBMS,

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

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). PostGIS is ...

SQL Anywhere SAP SQL Anywhere is a proprietary relational database management system (RDBMS) product from SAP. SQL Anywhere was known as Sybase SQL Anywhere prior to the acquisition of Sybase by SAP. History The database company Sybase obtained the SQL An ...

and

Vertica Vertica 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 CEOs 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 (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"">quot;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 descri ...

— 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 with more than 13000 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.org
- Official EPSG Geodetic Parameter Dataset webpage. 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