[geodesy]
A horizontal geodetic datum that serves as a basis for measurements over a limited area of the earth; with its origin at a location on the earth's surface. It uses an ellipsoid whose dimensions conform well to its region of use. It was originally defined for land-based surveys. A local datum in this sense stands in contrast to a geocentric datum. Examples include the North American Datum of 1927 and the Australian Geodetic Datum of 1966.
[geodesy]
A horizontal or vertical datum used for measurements over a limited area of the earth, such as a nation, a supranational region, or a continent. A horizontal datum that is local in this sense may or may not be geocentric. For example, the North American Datum of 1983 and the Geocentric Datum of Australia 1994 are local in that they are applied to a particular part of the world; they are also geocentric. All vertical datums are local in that there is, at present, no global vertical datum.