National Geodetic Vertical Datum (NGVD) 4
National Geodetic Vertical Datum (NGVD) 4 : the national vertical datum, whose standard was established in 1929, and was used by the National Flood Insurance Program (NFIP) as the vertical control for its mapping from the Nil's inception in 1968 until approximately 2006 in Maine. NGVD is based upon mean sea level and also has been called "1929 Mean Sea Level (MSL)"
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