Datum point8/22/2023 ![]() The datum declares the Meades Ranch Triangulation Station in Osborne County, Kansas to be 39☁3′26.686″ north latitude, 98☃2′30.506″ west longitude. The North American Datum of 1927 (NAD 27) was based on surveys of the entire continent from a common reference point that was chosen in 1901, because it was as near the center of the contiguous United States as could be calculated: It was based on a triangulation station at the junction of the transcontinental triangulation arc of 1899 on the 39th parallel north and the triangulation arc along the 98th meridian west that was near the geographic center of the contiguous United States. North American Datum of 1927 Īs more data were gathered, discrepancies appeared, so the datum was recomputed in 1927, using the same spheroid and origin as its predecessor. ![]() In 1913, Canada and Mexico adopted that datum, so it was also renamed the North American Datum. ![]() It was fitted to data previously collected for regional datums, which by that time had begun to overlap. In 1901 the United States Coast and Geodetic Survey adopted a national horizontal datum called the United States Standard Datum, based on the Clarke Ellipsoid of 1866. NAD 83, along with NAVD 88, is set to be replaced with a new GPS- and gravimetric geoid model-based geometric reference frame and geopotential datum in 2022. Vertical measurements, based on distances above or below Mean High Water (MHW), are calculated using the North American Vertical Datum of 1988 (NAVD 88). Both are geodetic reference systems based on slightly different assumptions and measurements. In surveying, cartography, and land-use planning, two North American Datums are in use for making lateral or "horizontal" measurements: the North American Datum of 1927 (NAD 27) and the North American Datum of 1983 (NAD 83). A datum is a formal description of the shape of the Earth along with an "anchor" point for the coordinate system. The North American Datum ( NAD) is the horizontal datum now used to define the geodetic network in North America.
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