The Sea Level Datum of 1929 was the vertical control datum established for vertical control surveying in the United States of America by the General Adjustment of 1929. The datum was used to measure elevation or altitude above, and depression or depth below, mean sea level (MSL). It has been suggested that this article or section be merged with Geodetic system. ... Surveyor at work with a leveling instrument. ... Elevation histogram of the surface of the Earth – approximately 71% of the Earths surface is covered with water. ... Altitude is the elevation of an object from a known level or datum. ... This article needs to be wikified. ... Look up depth in Wiktionary, the free dictionary In classical physics, depth is a distance measured vertically from top to bottom (height) or horizontally from outside to inside (thickness). ... For considerations of sea level change, in particular rise associated with possible global warming, see sea level rise. ...

Mean sea level was measured at 26 tide gauges: 21 in the United States and 5 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. The adjustment required a total of 66,315 miles (106,724 km) of leveling with 246 closed circuits and 25 circuits at sea level.

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. Therefore, it was renamed the National Geodetic Vertical Datum of 1929 (NGVD 29) in 1973. The NGVD 29 was subsequently replaced by the North American Vertical Datum of 1988 (NAVD 88) based upon the General Adjustment of the North American Datum of 1988. For considerations of sea level change, in particular rise associated with possible global warming, see sea level rise. ... The GOCE project will measure high-accuracy gravity gradients and provide an accurate geoid model based on the Earths gravity field. ... In Mathematics and Physics (especially Electronics), a region is called equipotential if every point in it is at the same potential. ... The Sea Level Datum of 1929 was the vertical control datum established for vertical control surveying in the United States of America by the General Adjustment of 1929. ... The North American Vertical Datum of 1988 (NAVD 88) is the vertical control datum established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988. ...

See also

• altitude
• datum
• geodesy
• mean sea level
• North American Vertical Datum of 1988
• topographic elevation
• topography

Altitude is the elevation of an object from a known level or datum. ... It has been suggested that this article or section be merged with Geodetic system. ... Geodetic pillar (1855); Ostend, Belgium Archive with lithography plates for maps of Bavaria in the Landesamt für Vermessung und Geoinformation in Munich Geodesy (IPA North American English ; British, Australian English etc. ... For considerations of sea level change, in particular rise associated with possible global warming, see sea level rise. ... The North American Vertical Datum of 1988 (NAVD 88) is the vertical control datum established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988. ... Elevation histogram of the surface of the Earth – approximately 71% of the Earths surface is covered with water. ... For discussion of land surfaces themselves, see Terrain. ...

External links

• National Geodetic Survey website
  • Geodetic Glossary @ NGS
  • NGVD 29 to NAVD 88 online elevation converter @ NGS
• United States Geological Survey website