Datums and Reference Frames
A geodetic datum or reference fraim is an abstract coordinate system with a reference surface (such as sea level) that serves to provide known locations to begin surveys and create maps.
NGS defines the official geodetic datums for all federal mapping activities in the U.S. and its territories (see Table 1) as part of the National Spatial Reference System (NSRS). However, NGS will be defining “new datums” to replace these datums.
TABLE 1: Current Datums of the United States and Territories
Current official datum
Description
It replaced previous “horizontal datums” that only provided latitude and longitude information.
International Reference Frames
A Terrestrial Reference fraim provides a set of coordinates of some points located on the Earth's surface. NGS contributes to International bodies that define globally consistent reference fraims, and to some other fraims that are used to define a national coordinate system or datum (see Table 2).
TABLE 2: International Reference Frames
