# Coordinate reference system

Coordinates in the OFDS data model must be specified in the coordinate reference system (CRS) [required by GeoJSON](https://datatracker.ietf.org/doc/html/rfc7946#section-4):

> The coordinate reference system for all GeoJSON coordinates is a geographic coordinate reference system, using the World Geodetic System 1984 [WGS 84](https://datatracker.ietf.org/doc/html/rfc7946#ref-WGS84) datum, with longitude and latitude units of decimal degrees. This is equivalent to the coordinate reference system identified by the Open Geospatial Consortium (OGC) URN urn:ogc:def:crs:OGC::CRS84.

The CRS is referenced by the network-level `crs/name` and `crs/uri` properties, which must be set to the following values:

- `name`: urn:ogc:def:crs:OGC::CRS84
- `uri`: <http://www.opengis.net/def/crs/OGC/1.3/CRS84>

`urn:ogc:def:crs:OGC::CRS84` denotes WGS84 with the order longitude, latitude. It is equivalent to EPSG:4326 with reversed axes.

For more information, see [How to transform coordinates to the correct coordinate reference system](../guidance/publication.md#how-to-transform-coordinates-to-the-correct-coordinate-reference-system).