The new adjustment of the North American horizontal datum



Geodesy, like astrometry, was a highly precise science when other branches of geophysics were still in their infancy. Over continental distances, surveys reached levels of precision of the order of a part in 100,000. The burden of extensive hand computation was the limiting factor applied to the field. Geocentric coordinates and ties between continents were less well known; the uncertainties were 200 m or more. One of the major scientific achievements of its day was the North American 1927 Datum, compiled by the U.S. Coast and Geodetic Survey. The coordinates of points in the contiguous 48 states and parts of Canada were adjusted and put into a single system with a high degree of internal consistency. Chord lengths determined by satellite methods have verified the quality of the work [Marsh et al., 1973].