EPSGcodes

EPSG codes are numerical identifiers assigned to components of the geodetic parameter dataset maintained under the EPSG registry. The dataset catalogs coordinate reference systems (CRS), datums, ellipsoids, unit definitions, and coordinate operations used to define how geographic positions are projected and measured on the Earth. Each entry receives a unique code, typically written as EPSG:NNNN, and is accompanied by descriptive metadata and parameters such as projection method, datum, and unit.

The EPSG registry includes both geographic and projected CRSs, in 2D and 3D forms, as well as transformations between CRSs. Examples include EPSG:4326 for WGS 84 geographic coordinates and EPSG:3857 for WGS 84 / Pseudo-Mercator. The codes are used across GIS software, databases, and metadata to ensure consistent interpretation of spatial data. The registry also contains definitions for ellipsoids, datums, coordinate axes, and area-of-use information.

Maintenance and governance: the EPSG dataset originated with the European Petroleum Survey Group and is maintained by the International Association of Oil & Gas Producers (IOGP) in collaboration with the geospatial community. The official EPSG registry is hosted at epsg.org and is periodically updated to add new codes or refine existing definitions. Software libraries such as PROJ, GDAL, and various GIS applications rely on the EPSG registry to translate between human-readable CRS descriptions and machine-readable parameters.

In use, data producers tag datasets with an EPSG code in metadata or headers, enabling interoperable data exchange and precise coordinate interpretation. See also: geodetic parameter dataset, coordinate reference system, PROJ, EPSG registry.