North American Datum

Information about North American Datum

The North American Datum is the official datum used for the primary geodetic network in North America. In the fields of cartography and land-use there are currently two North American Datums in use: the North American Datum of 1927 (NAD 27) and the 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 geodetic "center" of NAD-27 is a base station at Meades Ranch in Kansas.

North American Datum of 1983

As satellite and remote sensing technology both improved and were made available for civilian applications, it became obvious that the NAD-27's appromixations were not sufficiently accurate.

The North American Datum of 1983 was created to meet requirements for better accuracy and more precision. It is based on the GRS80 ellipsoid; an ellipsoid derived from satellite geodesy.

EllipsoidSemi-major axisEccentricity Squared
NAD 836,378,137 m0.006694300229

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 specify the datum along with the coordinates. The North American Datum of 1927 is defined by the latitude and longitude of an initial point (Meades Ranch in Kansas), the direction of a line between this point and a specified second point, and two dimensions that define the spheroid. The North American Datum of 1983 is based on a newer 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
This article describes a concept from surveying and geodesy. Datum is also the last known position of a submarine in ASW, the singular form of data, and a city in ancient Macedonia, probably on the site of the modern Kavala.

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Geodesy (IPA North American English /dʒiˈɑdɪsi/; British, Australian English etc. /dʒɪˈɒdəsi/), also called geodetics
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Alexander Ross Clarke (1828-1914) was a British geodesist, primarily remembered for his work defining different reference ellipsoids approximating the shape of the geoid.

Clarke was born on December 16, 1828 in Reading, Berkshire, England.
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In geodesy, a reference ellipsoid is a mathematically-defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body. Because of their relative simplicity, reference ellipsoids are used as a preferred surface on which geodetic network
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Meades Ranch in Kansas is designated as the geodetic base point for the North American Datum of 1927 (NAD 27) at (39.224079, -98.541807). This is at or very near the geographic center of the forty-eight contiguous U.S. states.
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satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.
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remote sensing is the short or large-scale acquisition of information of an object or phenomenon, by the use of either recording or real-time sensing device(s) that is not in physical or intimate contact with the object (such as by way of aircraft, spacecraft, satellite, buoy, or
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A civilian under international humanitarian law is a person who is not a member of his or her country's armed forces. The term is also often used colloquially to refer to people who are not members of a particular profession or occupation, especially by law enforcement agencies,
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satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.
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Geodesy (IPA North American English /dʒiˈɑdɪsi/; British, Australian English etc. /dʒɪˈɒdəsi/), also called geodetics
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Meades Ranch in Kansas is designated as the geodetic base point for the North American Datum of 1927 (NAD 27) at (39.224079, -98.541807). This is at or very near the geographic center of the forty-eight contiguous U.S. states.
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spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. Three particular cases of a spheroid are:
  • If the ellipse is rotated about its major axis, the surface is a prolate spheroid

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