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Military Grid Reference System

Description

The Military Grid Reference System (MGRS) and the U.S. National Grid (USNG), an MGRS derived product are, gridded reference systems that describe areas of the Earth based on the Universal Transverse Mercator (UTM) coordinate system between latitudes 84° N and 80°S and the Universal Polar Stereographic (UPS) system for areas north of 84° N and south of 80°S. They use the metric measurement system, widely adopted throughout the world, and report position as distance from the equator (Northing) and distance from the zone central meridian (Easting) following the convention used by the UTM coordinate system. 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 spatially the same as MGRS but there are spaces in the USNG labeling structure that are not present in 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.

Strengths

The framework used by the Military Grid Reference System (MGRS) has the qualities needed for a grid standard that could be applicable to bird monitoring sampling. These qualities include:

1. Resolutions as fine as 1-meter cells, providing sufficient spatial precision for integrating data collected at most scales;

2. Use of squared cells;

3. Global extent for application to any area of the world;

4. Naming convention for grid cells based on multiples of 10 (e.g. 1, 10, 100, and 1000 meters).

6. Use of gridded coordinate system widely used by satellites and global positioning systems.

Weaknesses

Until recently, access to MGRS products at scales finer than 100 km were difficult to acquire because they are administered primarily by the National Geospatial Intelligence Agency. Efforts are currently underway through a partnership among American Bird Conservancy, Rocky Mountain Bird Observatory, USGS, and the University of Florida to generate 100 m and 1 km MGRS products for portions of the Western Hemisphere on an as-needed basis. Grids for North America are now available at 100 m, 1 km, 10 km, and 100 km scales from http://mgrs-data.org/.

Examples of use

MGRS has a long history of use by the U.S. military forces. It is also increasingly being used for emergency planning around the world.

For more information

http://mgrs-data.org/

http://en.wikipedia.org/wiki/Military_grid_reference_system 

A naming convention exists for the USNG and MGRS cells and is described here:

http://www.andrewlesley.freeserve.co.uk/gps/UTMMGRS.html

http://earth-info.nga.mil/GandG/coordsys/grids/referencesys.html