datum (geodetic)

datum (geodetic)

1. A reference surface consisting of five quantities: the latitude and longitude of an initial point, the azimuth of a line from that point, and the parameters of the reference ellipsoid.
2. The mathematical model of the earth used to calculate the coordinates on any map. Different nations use different datums for printing coordinates on their maps. The datum is usually referenced in the marginal information of each map.
Dictionary of Military and Associated Terms. US Department of Defense 2005.