EPSG code

A standard numeric identifier for a coordinate reference system (e.g., 4326 for WGS84 lon/lat).

Category: CRS & Coordinates · Also known as: CRS code, SRID code, EPSG identifier

Definition (expanded)

EPSG codes are widely used to reference CRS definitions consistently across tools and databases. In PostGIS, the same number is often called SRID. Knowing the correct EPSG code is key for correct transformations and measurements.

Common mistakes

Guessing the CRS from coordinate ranges without checking metadata.
Mixing EPSG:4326 and EPSG:3857 coordinates in the same workflow.

Related terms

SRIDA numeric identifier for a coordinate reference system used by some databases and formats (especially PostGIS and EWKB).CRS (Coordinate Reference System)A definition of how coordinates map to real locations on Earth, including projection, datum, and units.EPSG:4326 (WGS84 lon/lat)A common coordinate reference system using longitude/latitude on WGS84.Web Mercator (EPSG:3857)A common projected CRS used by web maps; it distorts area and shape but is fast and convenient for tiles.UTM (Universal Transverse Mercator)A projected coordinate system split into zones, commonly used for accurate local measurements in meters.Reprojection (coordinate transformation)Converting coordinates from one CRS to another (e.g., EPSG:4326 lon/lat → EPSG:3857 meters).Datum (geodetic datum)The Earth model a CRS is based on; different datums can shift coordinates even if units look the same.