Maps GPS Glossary - N

NAD 27 - North American Datum 1927

NAD 83 - North American Datum 1983

nadir - A point on the celestial sphere directly below the observer, diametrically opposite the zenith.

nala - A ravine.

National Differential Global Positioning System - A network of ground- and beacon-based differential stations that increases GPS accuracy.

National Marine Electronics Association - A US standards committee that defines the data message structure, contents, and protocols that allow GPS receivers to communicate with other electronic equipment.

nautical mile - a unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle - equal to appr. 1852 meters (6076 feet).

NAVD 88 - Vertical reference system (elevation) for U.S., Canada, and Mexico; orthometric heights are derived from a particular point on the St. Lawrence Seaway.

NAVSTAR (Navigation Satellite Timing and Ranging) - The name given to the system of GPS satellites.

NDGPS - Nationwide DGPS.

neatline - Line separating the body of a map from the map margin. On a standard quadrangle map, the neatlines are the meridians and parallels delimiting the quadrangle.

NGS - National Geodetic Survey - An agency of the United States NOAA that defines and manages a national coordinate system. This network, the National Spatial Reference System (NSRS), provides the foundation for transportation and communication; mapping and charting; and a multitude of scientific and engineering applications.

NMEA - see National Marine Electronics Association

NSDI - National Spatial Data Infrastructure - The set of base geographic data necessary for effective operation of the United States federal government and its suppliers, made accessible as a distributed database.

NSRS - National Spatial Reference System - A system administered by the NGS that provides the foundation for transportation and communication; mapping and charting; and a multitude of scientific and engineering applications.

nullah - See nala.