Local Datum Definition | GIS Dictionary

local datum

[geodesy] A horizontal or vertical datum used for measurements over a limited area of the earth, such as a nation or a continent. It uses a reference ellipsoid with dimensions that conform well to the region of use. The concept of a local datum was originally defined for land-based surveys.
A horizontal local datum may be geodetic, using a limited reference ellipsoid that conforms to the region of use, or geocentric, using the entire earth at the center of the reference ellipsoid. Examples of horizontal geodetic local datums include the North American Datum of 1927 and the Australian Geodetic Datum of 1966. Examples of horizontal geocentric local datums include the North American Datum of 1983 and the Geocentric Datum of Australia 1994. All vertical datums are local in that there is, at present, no global vertical datum.