MGRS vs UTM

MGRS uses a system of numbers and letters to display UTM coordinates.

The Maryland state house is at N38°58.739' W76°29.456' in Annapolis. Coordinates always read "Right, Up", with x first and then y.  This contrasts with lat/long, which generally have latitude (y) first.

 UTM--Universal Transverse Mercator UTM Zone Hemisphere false easting (m) northing (m) 1-60 N,S 100,000-900,000 0--10,000,000 18 N 370823 4315291

UTM coordinates may be given as 18N 370823E 370823N, but there is no absolute standard. Easting is generally given first.

UTM has a false easting of 500,000 at the central meridian of each UTM zone, and a false northing in the southern hemisphere.  These allow UTM coordinates to avoid negative numbers.

 MGRS--Military Grid Reference System UTM Zone Lat Band 100K grid square easting northing Accuracy 1-60 C-X (No I, O) 18 S UJ 70823 15291 1 meter 18 S UJ 7082 1529 10 meters 18 S UJ 708 152 100 meters 18 S UJ 71 15 1000 meter 18 S UJ 7 1 10 km

MGRS is given as one continuous string, and the user knows how to break it up. This example would be 18SUJ7082315291, or 18SUJ70821529, or 18SUJ708152. The easting and northing are always given to the same level of accuracy, so that the last portion of a MGRS coordinate always has an even number of digits after the two letters of the 100K grid square.

The 100K grid squares use the letters C to X; they omit the letters I and O to avoid confusion with the numbers 1 and 0.  Letters A and B are used for the South Pole and Y-Z are used for the North Pole in the polar stereographic projection.

Note that MGRS eastings and northings omit one digit on the easting (3 in this case), and generally two on the northing (43 in this case; it would be one digit very close to the equator in the northern hemisphere), which are included with the 100K grid letters.

When dealing with a small area when all concerned know the region, you can omit the UTM Zone and Lat Band, and for even smaller areas you can also omit the 100K grid square. In that case you could transmit 6, 8, or 10 digit coordinates depending on the accuracy required.

 On military maps, the grid typically shows two coordinates in both the x and y directions.  They are indicated in the margins, and often within the main part of map centered on some grid lines.

MGRS zones.

The US National Grid (USNG) is actually MGRS.

UTM projection

Last revision 9/16/2015