All geographic data is created in some coordinate system, and in the context of some . A datum includes information and a datum definition. For example, the Gauss-Kruger Conformal projection system used in Germany uses the Bessel ellipsoid and Potsdam datum definition. Some coordinate systems only specify the ellipsoid; these are non-geodetic. Coordinate systems that specify the complete datum are geodetic.
Most of the coordinate systems supplied with AutoCAD Map 3D are geodetic, but about ten percent are non-geodetic. Therefore, you should determine whether the coordinate systems you use are geodetic or non-geodetic before you assign a coordinate system to a drawing. If you have data in a drawing that uses a non-geodetic coordinate system, but do not know what datum the data came from, you might introduce errors if you convert the drawing to a geodetic coordinate system.