Why not just use National Geodetic Vertical Datum of 1929 (NGVD29) for everything?
During the early part of the twentieth century it was assumed that global sea level was everywhere the same. In 1929 a general adjustment of benchmarks was conducted to obtain a best fit of mean sea level observations at 26 tide stations in the United States and Canada. It was subsequently discovered that global mean sea level is not the same throughout the oceans. Moreover, the national benchmark network has been extensively expanded subsequent to 1929 and both subsidence and isostatic rebound have occurred in the continental US. The result is, that based upon the North American adjustment of 1988 (NAVD88), the Atlantic coastline is about 30cm below NGVD29 and the Rocky Mountains and westward to the Pacific coast is about 100cm higher than NGVD29. Use of NGVD29 would result in gross elevation errors everywhere except perhaps locations in the central Mississippi Valley. Back to top 12. How does one determine the relationship between NGVD-1929 and NAVD-1988? The methodology used to shif
