What are NAD 27 and NAD 83?
The North American Datum of 1927 (NAD 27) is “The horizontal control datum for the United States that (was) defined by (a) location and azimuth on the Clarke spheroid of 1866, with origin at (the survey station) Meades Ranch.” … The geoidal height at Meades Ranch (was) assumed to be zero. “Geodetic positions on the North American Datum of 1927 were derived from the (coordinates of and an azimuth at Meades Ranch) through a readjustment of the triangulation of the entire network in which Laplace azimuths were introduced, and the Bowie method was used.” (Geodetic Glossary, pp. 57) The North American Datum of 1983 (NAD 83) is “The horizontal control datum for the United States, Canada, Mexico, and Central America, based on a geocentric origin and the Geodetic Reference System 1980. “This datum, designated as NAD 83, is the new geodetic reference system. … NAD 83 is based on the adjustment of 250,000 points including 600 satellite Doppler stations which constrain the system to a geocent
