National Geodetic Vertical Datum of 1929

Originally known as Sea Level Datum of 1929, NGVD 29 was determined and published by the United States Coast and Geodetic Survey[2] and used to measure the elevation of a point above and depression below mean sea level (MSL).NGVD29 was superseded by the North American Vertical Datum of 1988 (NAVD 88),[3] based upon reference to a single benchmark (referenced to the new International Great Lakes Datum of 1985 local mean sea level height value), although many cities and U.S. Army Corps of Engineers "legacy" projects with established data continued to use the older datum.[4] Mean sea level was measured at 26 tide gauges: 21 in the United States and five in Canada.The datum was defined by the observed heights of mean sea level at the 26 tide gauges and by the set of elevations of all bench marks resulting from the adjustment of observations.Since the Sea Level Datum of 1929 was a hybrid model, it was not a pure model of mean sea level, the geoid, or any other equipotential surface.
Illustration of vertical datums in the United States.
GeodesyGeodynamicsGeomaticsHistoryGeographical distanceFigure of the EarthradiuscircumferenceGeodetic coordinatesGeodetic datumGeodesicHorizontal position representationLatitudeLongitudeMap projectionReference ellipsoidSatellite geodesySpatial reference systemSpatial relationsVertical positionsGlobal Nav. Sat. Systems (GNSSs)Global Pos. System (GPS)GLONASS (Russia)BeiDou (BDS) (China)Galileo (Europe)NAVIC (India)Quasi-Zenith Sat. Sys. (QZSS) (Japan)Discrete Global Grid and GeocodingNGVD 29OSGB36GRS 80ISO 6709WGS 84NAVD 88ETRS89GCJ-02Geo URIInternational Terrestrial Reference SystemSpatial Reference System Identifier (SRID)Universal Transverse Mercator (UTM)vertical datumsurveyingUnited States of AmericaUnited States Coast and Geodetic Surveyelevationdepressionmean sea levelNorth American Vertical Datum of 1988U.S. Army Corps of EngineersCanadaadjustment of observationslevellingequipotentialNational Geodetic SurveyNational Oceanic and Atmospheric AdministrationAltitudeTopographyUnited States National Geodetic Survey