datumsystem
A datumsystem, in geodesy and cartography, is a reference framework used to assign coordinates to points on or near the Earth's surface for maps, surveys, and navigation. It defines the position of the origin, the orientation and shape of a reference surface (the ellipsoid) that approximates the Earth, and how coordinates relate to real locations. A datumsystem is typically part of a coordinate reference system, which may also include a map projection to convert curved surface coordinates into a flat map.
A datum comprises a geodetic datum (the mathematical model of the Earth), a reference ellipsoid (an idealized
Datumsystems are categorized as global or local. Global geodetic datums, such as WGS84, serve worldwide positioning
Because the Earth is dynamic, datums can drift over time, especially global systems tied to plate tectonics.