Military Grid Reference System

The Military Grid Reference System (MGRS) is the geocoordinate standard used by NATO militaries for locating points on the earth. The MGRS is derived from the Universal Transverse Mercator (UTM) grid system and the Universal Polar Stereographic (UPS) grid system, but uses a different labeling convention. The MGRS is used for the entire earth.

An example of an MGRS coordinate, or grid reference, would be 4QFJ12345678, which consists of three parts:

• 4Q (grid zone designator, GZD),
• FJ (the 100,000-meter square identifier), and
• 12345678 (numerical location; easting is 1234 and northing is 5678, in this case specifying a location with 10 m resolution).

An MGRS grid reference is a point reference system. When the term 'grid square' is used, it can refer to a square with a side length of 10 km (6 mi), 1 km, 100 m (328 ft), 10 m or 1 m, depending on the precision of the coordinates provided. (In some cases, squares adjacent to a Grid Zone Junction (GZJ) are clipped, so polygon is a better descriptor of these areas.) 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 polygon will remain within the boundaries of the less precise polygon. Related to this is the primacy of the southwest corner of the polygon being the labeling point for an entire polygon. 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.

• 4Q ...................GZD only, precision level 6° × 8° (in most cases)
• 4QFJ .................GZD and 100 km SQ_ID, precision level 100 km
• 4QFJ16 ...............precision level 10 km
• 4QFJ1267 .............precision level 1 km
• 4QFJ123678 ...........precision level 100 m
• 4QFJ12346789 .........precision level 10 m
• 4QFJ1234567890 .......precision level 1 m

Such an MGRS coordinate, standing alone, may be converted to latitude and longitude. But you still do not know the position on the Earth, unless you also know the geodetic datum that is used.