Universal Transverse Mercator (UTM) and Military Grid Reference
The AFE grid is modified from the Military Grid Reference System
(MGRS). The MGRS itself is an alphanumeric version of a numerical
UTM (Universal Transverse Mercator) or UPS (Universal Polar Stereographic)
grid coordinate. Here is a short explanation of the UTM and MGRS.
Universal Transverse Mercator (UTM)
- Projection: Transverse Mercator (Gauss-Krüger type) in zones
- Longitude of Origin: Central meridian (CM) of each projection
zone (3°, 9°, 15°, 21°, 27°, 33°, 39°,
45°, 51°, 57°, 63°, 69°, 75°, 81°, 87°,
93°, 99°, 105°, 111°, 117°, 123°, 129°,
135°, 141°, 147°, 153°, 159°, 165°, 171°,
177°, E and W).
- Latitude of Origin: 0° (the Equator).
- Unit: Meter.
- False Northing: 0 meters at the Equator for the Northern Hemisphere;
10,000,000 meters at the Equator for the Southern Hemisphere.
- False Easting: 500,000 meters at the CM of each zone.
- Scale Factor at the Central Meridian: 0.9996.
- Latitude Limits of System: From 80°S to 84°N.
- Limits of Projection Zones: The zones are bounded by meridians,
the longitudes of which are multiples of 6° east and west of
the prime meridian.
Universal Transverse Mercator (UTM) coordinates define two dimensional,
horizontal, positions. The sixty UTM zone numbers designate
6 degree wide longitudinal strips extending from 80 degrees South
latitude to 84 degrees North latitude. UTM zone characters
are letters which designate 8 degree zones extending north and south
from the equator. Beginning at 80° south and proceeding northward,
twenty bands are lettered C through X, omitting I and O. These bands
are all 8° wide except for bond X which is 12° wide (between
There are special UTM zones between 0 degrees and 36 degrees longitude
above 72 degrees latitude and a special zone 32 between 56 degrees
and 64 degrees north latitude:
- UTM Zone 32 has been widened to 9° (at the expense of zone
31) between latitudes 56° and 64° (band V) to accommodate
southwest Norway. Thus zone 32 it extends westwards to 3°E in
the North Sea.
- Similarly, between 72° and 84° (band X), zones 33 and
35 have been widened to 12° to accommodate Svalbard. To compensate
for these 12° wide zones, zones 31 and 37 are widened to 9°
and zones 32, 34, and 36 are eliminated. Thus the W and E boundaries
of zones are 31: 0 - 9 E, 33: 9 - 21 E, 35: 21 - 33 E and 37: 33
- 42 E.
Fig. 1: MGRS zones
Military Grid Reference System (MGRS)
Table 1. MGRS scheme (also
available as an Excel table).
The Military Grid Reference System (MGRS) is an extension of the
UTM system. UTM zone number and zone character are used to identify
an area 6 degrees in east-west extent and 8 degrees in north-south
extent. UTM zone number and designator are followed by 100 km square
easting and northing identifiers. The system uses a set of alphabetic
characters for the 100 km grid squares. Starting at the 180 degree
meridian the characters A to Z (omitting I and O) are used for 18
degrees before starting over. From the equator north the characters
A to V (omitting I and O) are used for 100 km squares, repeating every
2,000 km. Northing designators normally begin with 'A' at the equator
for odd numbered UTM easting zones.
For even numbered easting zones the northing designators are offset
by five characters, starting at the equator with 'F'. South of the
equator, the characters continue the pattern set north of the equator.
Complicating the system, ellipsoid junctions (spheroid junctions in
the terminology of MGRS) require a shift of 10 characters in the northing
100 km grid square designators. Different geodetic datums using different
reference ellipsoids use different starting row offset numbers to
If 10 numeric characters are used, a precision of 1 meter is assumed.
2 characters imply a precision of 10 km. From 2 to 10 numeric characters
the precision changes from 10 km, 1 km, 100 m 10 m, to 1 m.
MGRS 100,000-meter square identification
- The 100,000-meter columns, including partial columns along zone,
datum, and ellipsoid junctions, are lettered alphabetically, A through
Z (with I and O omitted), north and south of the Equator, starting
at the 180° meridian and proceeding easterly for 18°. The
alphabetical sequence repeats at 18° intervals.
- To prevent ambiguity of identifications along ellipsoid junctions
changes in the order of the row letters are necessary. The row alphabet
(second letter) is shifted ten letters. This decreased the maximum
distance in which the 100,000-meter square identification is repeated.
- The 100,000-meter row lettering is based on a 20-letter alphabetical
sequence (A through V with I and O omitted). This alphabetical sequence
is read from south to north, and repeated at 2,000,000-meter intervals
from the Equator.
- The row letters in each odd numbered 6° grid zone are read
in an A through V sequence from south to north.
- In each even-numbered 6° grid zone, the some lettering sequence
is advanced five letters to F, continued sequentially through V
and followed by A through V.
- The advancement or staggering of row letters for the even-numbered
zones lengthens the distance between 100,000-meter squares of the
- Deviations from the preceding rules were mode in the past. These
deviations were an attempt to provide unique grid references within
a complicated and disparate world-wide mapping system.
- Determination of 100,000-meter grid square identification is further
complicated by the use of different ellipsoids.
The military grid reference
The MGRS coordinate for a position consists of a group of letters
and numbers which include the following elements:
- The Grid Zone Designation.
- The 100,000-meter square letter identification.
- The grid coordinates (also referred to as rectangular coordinates);
the numerical portion of the reference expressed to a desired refinement.
- A reference is written as an entity without spaces, parentheses,
dashes, or decimal points.
- 18S (Locating a point within the Grid Zone Designation)
- 18SUU (Locating a point within a 100,000-meter square)
- 18SUU80 (Locating a point within a 10,000-meter square)
- 18SUU8401(Locating a point within a 1,000-meter square)
- 18SUU836014(Locating a point within a 100-meter square)
To satisfy special needs, a reference can be given to a 10-meter
square and a 1-meter square as:
- 18SUU83630143 (Locating a point within a 10-meter square)
- 18SUU8362601432(Locating a point within a 1-meter square)