CRSS

CRSs stands for Coordinate Reference Systems, a framework used in geodesy and geospatial analysis to locate geographic features on the Earth's surface. A CRS defines how coordinates are measured and related to the real world, including a datum, a projection, and a coordinate system. Datums establish the reference surface (for example, WGS 84, NAD83, or ETRS89). Projections convert the curved surface of the Earth to a flat plane, introducing distortions in area, shape, distance, or direction; common projections include UTM zones, Mercator, and Lambert Conformal Conic. Geographic coordinate systems express positions with latitude and longitude on a datum, while projected coordinate systems express planar coordinates in units such as meters. The EPSG Geodetic Parameter Dataset catalogues thousands of CRSs to support interoperability.

Choosing a CRS depends on the region of interest and the task. For global datasets, a geographic CRS or a globally appropriate projected CRS may be used; for local mapping, a projection optimized for the area minimizes distortion. Transformations between CRSs are common and may involve datum shifts (Helmert transformations) or more complex methods. Geographic Information Systems can perform on-the-fly reprojection to align layers in different CRSs, and users often publish data with explicit CRS metadata to avoid misalignment.

See also: EPSG, GIS, cartography.