What does the term “G.S.V.D.” mean in determining the level of Lake Okeechobee?

The term G.S.V.D. means Geodetic Survey Vertical Datum of 1929.  Before 1929, all maps were prepared with elevations based on “mean Sea Level Datum of 1929.” In the 1970’s, the name was changed to the National Geodetic Vertical Datum (NGVD) of 1929. One of the reasons for the name change was that it was found that the sea is actually not level.Jul 26, 2013.