navd

The North American Vertical Datum of 1988 (NAVD 88) is a geodetic vertical datum used in the United States, Canada, Mexico, and the Caribbean. It is a realization of the North American Vertical Datum of 1988, which is a geodetic datum for vertical control. The datum is based on a geoid model derived from a combination of gravity data and GPS observations. The NAVD 88 datum is used to establish vertical control points, which are used to determine the elevation of features on the Earth's surface. The datum is used in a variety of applications, including surveying, mapping, and engineering. The NAVD 88 datum is maintained by the National Geodetic Survey (NGS) in the United States and by similar organizations in other countries. The datum is periodically updated to reflect changes in the Earth's gravity field and to improve the accuracy of vertical control points. The NAVD 88 datum is an important tool for ensuring the accuracy and consistency of vertical control in North America.