Meades Ranch in Kansas is designated as the geodetic base point for the North American Datum of 1927 (NAD 27) at 39°13′26.686″N 98°32′30.506″W / 39.22407944°N 98.54180722°W (39.224079, -98.541807). This is at or very near the geographic center of the forty-eight contiguous U.S. states. The base point was the reference point for almost all land survey measurements in the United States from 1927 until the establishment of the North American Datum of 1983 (NAD 83) and the World Geodetic System of 1984 (WGS84). NAD 27 was based on the Clarke Ellipsoid of 1866.
A reference ellipsoid is a mathematical construct designed to closely match the actual shape of the earth – the geoid. Calculations for map projections are performed using the parameters of the ellipsoid. The geoid, being irregular, is impossible to precisely model mathematically. For the purpose of the NAD 27, the geoidal height at Meades Ranch was assumed to be zero so that the geoid and the ellipsoid coincide at that point.
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