Glossary Terms

Glossary Entries Sorted by Beginning Letter

N

nadir

The line extending perpendicularly from an aerial camera to a point on the ground. If the camera and airplane are perfectly level (without pitch or tilt), the nadir point will be the same as the principal point.

See Also: principal point

National Aerial Photography Program (NAPP)

USGS program established to coordinate the collection of aerial photography covering the 48 contiguous states and Hawaii every five years.

National Digital Orthophoto Program (NDOP)

Program proposed in 1990 by the USDA and USGS to ensure the public domain availability of digital orthophoto quadrangle (DOQ) data for the nation.

National Geodetic Vertical Datum of 1929 (NGVD 29)

A geodetic reference for elevations, completed and adjusted in 1929. These elevations were used to define the mean sea level datum. This datum was replaced by NAVD 88.

See Also: North American Vertical Datum of 1988

National High Altitude Photography Program (NHAPP)

Origional name of NAPP

See Also: National Aerial Photography Program

National Map Accuracy Standards (NMAS)

Standards ensuring the accuracy of both map location (the latitude and longitude of a point) and elevation (the altitude above sea level).

More information on NMAS.

National Spatial Data Infrastructure (NSDI)

Established to promote sharing of geospatial data throughout all levels of governments, private and non-profit sectors, and the academic community

North American Datum of 1927 (NAD 27)

A geodetic reference for horizontal positions, established in 1927 and based on the Clark ellipsoid of 1866.

See Also: ellipsoid

North American Datum of 1983 (NAD 83)

A geodetic reference for horizontal positions, established in 1983 and based on the GRS 80 ellipsoid.

See Also: ellipsoid

North American Vertical Datum of 1988 (NAVD 88)

A geodetic reference for elevations, created by the NGS to replace the NGVD 29. This new datum was published in 1991, and incorporates vertical datums used on the Great Lakes. It is adjusted based on field work prior to 1929 as well as surveys as recent as 1988.

See Also: National Geodetic Vertical Datum of 1929

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