National Geodetic Vertical Datum (NGVD) of 1929

A geodetic datum established in 1929; previously used by FEMA as a basis for measuring flood, ground, and structural elevations.
Although NAVD datum is now used for Flood Insurance Rate Maps, NGVD is still used in many of the older FIRMs. NGVD was
previously referred to as Sea Level Datum or Mean Sea Level.