North American Datum

The North American Datum is the official reference ellipsoid used for the primary geodetic network in North America. Currently, in the fields of cartography and land-use; there are two North American Datums in use: North American Datum of 1927 (NAD 27) and North American Datum of 1983 (NAD 83). Both are geodetic reference systems, but each is based on different measurements.

North American Datum of 1927

The North American Datum of 1927 (NAD27) is a datum based on the Clarke Ellipsoid of 1866. This Ellipsoid was created by way of manual surveying of the entire continent. The geodectic "center" of NAD-27 is a base station at Meades Ranch in Kansas.

North American Datum of 1983

In the last 25 years, as satellite and remote sensing technology have both improved and made available for civilian applications it became obvious that the NAD-27's appromixations were no longer accurate for broader scopes.

The North American Datum of 1983 was created to respond to these changes. It is based on the GRS80 ellipsoid; an ellipsoid derived from satellite geodesy.

Comparisons Between NAD-27 and NAD-83

A point having a given latitude and longitude in NAD27 may be displaced on the order of many tens of meters from another point having the identical latitude and longitude in NAD83. So it is important to define your datum as well as your coordinates.The North American Datum of 1927 is defined by the latitude and longitude of an initial point (Meade's Ranch in Kansas), the direction of a line between this point and a specified second point, and two dimensions that define the spheroid. The new North American Datum of 1983 is based on a newly defined spheroid (GRS80); it is an Earth-centered datum having no initial point or initial direction

External links

• NADCON – a free utility to convert between NAD27 and NAD83
  • nadcon.prl – a web-based utility for NADCON

See also

• WGS-84

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