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U.S. National Grid

Description

The US National Grid (USNG) is a ground-based gridded coordinate system based on the Universal Transverse Mercator (UTM) System and derived from the Military Grid Reference System (MGRS). As such, the basic unit of measure is the meter and positions are reported as distance north from the equator (Northings) and distance from the zone central meridian (Eastings). It provides a nationally consistent language of location in a user friendly format. The purpose of USNG is to provide a seamless, standardized system of reference for nationwide use. The primary difference between  the MGRS and USNG is their datums, which describe the 3 dimensional  shape of the Earth. The MGRS uses the WGS84 datum and the USNG uses the NAD83 datum. When the USNG is used with the World Geodetic System of  1984 (WGS84) datum, it is exactly the same as MGRS. Otherwise, the  maximum offset between the datum is less than 2 meters (Natural  Resources Canada http://www.geod.nrcan.gc.ca/faq_e.php#23), which is negligible for most applications. Relationships among the UTM coordinate system, MGRS and USNG are described here: http://www.andrewlesley.freeserve.co.uk/gps/UTMMGRS.html

Strengths

The U.S. National Grid (USNG) (Federal Geographic Data Committee 2001), has the qualities needed for a grid standard that could be applicable to bird monitoring sampling. These qualities include:

  1. Sufficient spatial precision for integrating data collected at any scale (no minimum resolution);
  2. Use of squared cells;
  3. National extent for application to any area of the conterminous United States;
  4. Naming convention for grid cells based on multiples of 10 (e.g. 1, 10, 100, and 1000 meters).
  5. Use as a national standard grid in the United States with existing documentation issued by the Federal Geographic  Data Committee  (FGDC);
  6. Use of gridded coordinate system widely used by mapping programs such as the US National Map.

Weaknesses

The USNG is only available for the conterminous United States. 

Examples of use

The US National Grid is the standard set forth by the FGDC (http://www.fgdc.gov/usng) to "create a more favorable environment fo developing location-based services within the United States and to increase the interoperability of location services applicanced with printed map products by establishing a nationally consistent grid reference system as the preferred grid for the National Spatial Data Infrastructure".

For more information

The  USNG is currently available for online download as 1 km cell  products, with cells labeled by 1 km and 100 km name from The USNG  National Implementation Center (TUNIC) at Delta State University. These products   are organized by state and UTM zone: http://mississippi.deltastate.edu/