Maps GPS Glossary - N
NNN 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.
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