Military Grid Reference System
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The Military Grid Reference System (MGRS) is the geocoordinate standard used by NATO militaries for geo-referencing, position reporting, and situational awareness during land operations. An MGRS coordinate does not represent a single point, but rather identifies a square area (which can be as small as 1 m x 1 m) on the Earth's surface. The MGRS is derived from the Universal Transverse Mercator (UTM) and Universal Polar Stereographic (UPS) grid systems and is used as a geocode system for the entire Earth.
An example of an MGRS coordinate, or grid reference, is 4Q FJ 1234 6789, which consists of three parts:
4Q(grid zone designator, GZD)FJ(the 100,000-meter square identifier)1234 6789(numerical location; easting is1234and northing is6789, in this case specifying a location with 10 m resolution)
For machine-readability and database storage, all spaces may be removed.
An MGRS coordinate references a square or polygon on the Earth with a side length of 10 km, 1 km, 100 m, 10 m or 1 m, depending on the precision of the coordinates provided. (Certain squares adjacent to a Grid Zone Junction (GZJ) are clipped at an angle, resulting in a polygonal shape.)
| MGRS Coordinate | Precision (side length) |
|---|---|
4Q FJ |
100,000-meter square |
4Q FJ 1 6 |
10,000-meter square |
4Q FJ 12 67 |
1,000-meter square |
4Q FJ 123 678 |
100-meter square |
4Q FJ 1234 6789 |
10-meter square |
4Q FJ 12345 67890 |
1-meter square |
The number of digits in the numerical location must be even: 0, 2, 4, 6, 8 or 10, depending on the desired precision. When changing precision levels, it is important to truncate rather than round the easting and northing values to ensure the more precise square will remain within the boundaries of the less precise square.
Related to this is the primacy of the southwest corner of the square being the labeling point for the entire square. (In instances where the polygon is not a square and has been clipped by a grid zone junction, the polygon keeps the label of the southwest corner as if it had not been clipped.)
Google Maps recognizes MGRS grid references with one-meter square (10-digit numerical location) with spaces permitted only between the grid zone, the easting, and the northing (e.g., 4QFJ 12345 67890), and returns a dropped pin representing the centroid of the area referenced.