Military Grid Reference System: Difference between revisions

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{{Short description|NATO global coordinate reference system}}

{{Geodesy}}

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.<ref>{{cite nameweb |url="DMA8358_1_Chapter3">[httphttps://earth-infowww.ngajcs.mil/GandGPortals/publications36/tm8358.1Documents/tr83581bLibrary/Instructions/CJCSI%203900.html#ZZ26 DMA Technical Manual 835801E.1,pdf Chapter|title=CJCSI 33900.]01E Datums,Position Ellipsoids(POS), GridsNavigation, and Timing (PNT) and Global Positioning System (GPS) Requirements |publisher=Chairman of the Joint Chiefs of Staff |date=10 February 2023 |access-date=27 June 2025 |page=A-2 |quote=The Military Grid Reference SystemsSystem (MGRS) is the standard for military land operations for geo-referencing and position reporting.}}</ref> isAn theMGRS geocoordinatecoordinate standarddoes usednot byrepresent [[NATO]]a militariessingle forpoint, locatingbut areasrather defines a square grid area on the Earth's surface. The ___location of a specific point is therefore referenced by the MGRS coordinate of the area that contains it. The MGRS is derived from the [[Universal Transverse Mercator coordinate system|Universal Transverse Mercator]] (UTM)]] grid system and the [[Universal polarPolar stereographicStereographic coordinate system|Universal Polar Stereographic]] (UPS)]] grid system,systems but uses a different labeling convention. The MGRSand is used as a [[geocode]] for the entire Earth.

An example of an ''MGRS coordinate'', or ''grid reference'', would beis [{{Coor URL}}21_18_3421_24_35.0_N_157_55_043062452380_N_157_54_57.7_W_89102787040_W_&language=en 4QFJ12345678<code>4Q FJ 1234 6789</code>], which consists of three parts:

* <code>4Q</code> (grid zone designator, GZD)

* <code>FJ</code> (the 100,000-meter square identifier)

* <code>1234 56786789</code> (numerical ___location; [[Easting and northing|easting]] is <code>1234</code> and [[Easting and northing|northing]] is 5678<code>6789</code>, in this case specifying a ___location with 10&nbsp;m resolution)

For machine-readability and database storage, all spaces may be removed.

An MGRS grid reference represents a square area on the Earth's surface, rather than a single point.<ref>{{cite web |url=https://pro.arcgis.com/en/pro-app/latest/help/mapping/properties/military-grid-reference-system.htm |title=Military Grid Reference System |website=ArcGIS Pro |publisher=Esri |access-date=25 June 2025 |quote=An MGRS coordinate defines an area on the Earth's surface as opposed to a specific point.}}</ref> A ''grid square'' references a square on the Earth with a side length of 10&nbsp;km, 1&nbsp;km, 100&nbsp;m, 10&nbsp;m or 1&nbsp;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.)

An MGRS grid reference represents a square area on the Earth's surface, rather than a single point.<ref>{{cite web |url=https://pro.arcgis.com/en/pro-app/latest/help/mapping/properties/military-grid-reference-system.htm |title=Military Grid Reference System |website=ArcGIS Pro |publisher=Esri |access-date=25 June 2025 |quote=An MGRS coordinate defines an area on the Earth's surface as opposed to a specific point.}}</ref> A ''grid square'' references a square or polygon on the Earth with a side length of 10&nbsp;km, 1&nbsp;km, 100&nbsp;m, 10&nbsp;m or 1&nbsp;m, depending on the precision of the coordinates provided. (In some cases, squares adjacent to a Grid Zone Junction (GZJ) are clipped, so "polygon" ismay be a better descriptor of thesesuch 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 [[rounding|round]] the easting and northing values to ensure the more precise polygon will remain within the boundaries of the less precise polygon.

{| class="wikitable" style="text-align: left;"

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.

|+ MGRS precision levels

! MGRS Coordinate

! Precision (side length)

|-

| <code>4Q FJ</code>

| 100,000-meter square

|-

| <code>4Q FJ 1 6</code>

| 10,000-meter square

|-

| <code>4Q FJ 12 67</code>

| 1,000-meter square

|-

| <code>4Q FJ 123 678</code>

| 100-meter square

|-

| <code>4Q FJ 1234 6789</code>

| 10-meter square

|-

| <code>4Q FJ 12345 67890</code>

| 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 [[rounding|round]] the easting and northing values to ensure the more precise polygonsquare will remain within the boundaries of the less precise polygonsquare.

* 4Q ......................GZD only, precision level 6° × 8° (in most cases)

* 4Q FJ ...................GZD and 100&nbsp;km Grid Square ID, precision level 100&nbsp;km

Related to this is the primacy of the southwest corner of the polygonsquare being the labeling point for anthe entire polygonsquare. (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 FJ 1 6 ...............precision level 10&nbsp;km

* 4Q FJ 12 67 .............precision level 1&nbsp;km

[[Google Maps]] recognizes MGRS grid references which have a one-meter square precision (10-digit numerical ___location) with spaces permitted only between the 100,000-meter square, the easting, and the northing: e.g., <code>4QFJ 12345 67890</code>. The mapping application returns a dropped pin representing the [[centroid]] of the area referenced.

* 4Q FJ 123 678 ...........precision level 100&nbsp;m

* 4Q FJ 1234 6789 .........precision level 10&nbsp;m

* 4Q FJ 12345 67890 .......precision level 1&nbsp;m

==Grid zone designation==

[[File:Universal_Transverse_Mercator_zones.svg|thumb|300px|UTM zones on an equirectangular world map with irregular zones in red and New York City's zone highlighted]]

The first part of an MGRS coordinate is the ''grid-zone designation''. The 6° wide UTM zones, numbered 1–60, are intersected by latitude bands that are normally 8° high, lettered C–X (omitting I and O). The northmost latitude band, X, is 12° high. The intersection of a UTM zone and a latitude band is (normally) a 6° × 8° polygon called a ''grid zone'', whose ''designation'' in MGRS is formed by the zone number (one or two digits – the number for zones 1 to 9 is just a single digit, according to the example in DMA TM 8358.1, Section 3-2,<ref name="DMA8358_1_Chapter3">[http://earth-info.nga.mil/GandG/publications/tm8358.1/tr83581b.html#ZZ26 DMA Technical Manual 8358.1, Chapter 3.] Datums, Ellipsoids, Grids, and Grid Reference Systems</ref> Figure 7), followed by the latitude band letter (uppercase). This same notation is used in both UTM and MGRS, i.e. the UTM grid reference system; the article on [[Universal Transverse Mercator]] shows many maps of these grid zones, including the irregularities for Svalbard and southwest Norway.

As Figure 1 illustrates, Honolulu is in grid zone 4Q.

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One always reads map coordinates from west to east first (easting), then from south to north (northing). Common mnemonics include "in the house, up the stairs", "left-to-right, bottom-to-top" and "Read Right Up".

===Truncation, not rounding and read more===

As mentioned above, when converting UTM coordinates to an MGRS grid reference, or when abbreviating an MGRS grid reference to lower precision, onecoordinates shouldare {{em|truncatetruncated}}, and not rounded up (which would indicate the coordinates,next notadjacent round.grid Thissquare hasinstead beenof controversialthe insurrounding thesquare). past,

This sincewas once controversial as the oldest specification, TM8358.1,<ref name="DMA8358_1_Chapter3"/> usedindicated rounding, asand early versions didof GEOTRANS<ref name="Geotrans">[http://earth-info.nga.mil/GandG/geotrans/index.html GEOTRANS] Geographic Translator software and source code from the US National Geospatial-Intelligence Agency.</ref> beforefollowed version 3.0suit.

However, truncation ishas usedbeen applied in GEOTRANS since version 3.0, andas well as in NGA Military Map Reading 201<ref name="Military_Map_Reading_201"/> (page 5) and in the USU.S. Army Field Manual 3-25.26.<ref name="Field_Manual_3_25_26">[http://www.globalsecurity.org/military/library/policy/army/fm/3-25-26/index.html Map Reading and Land Navigation], U.S. Army Field Manual No. 3-25.26 (see section 4-6).</ref> The

Likewise, the civilian/continental version of MGRS, [[USNG]], also usesspecifies truncation.<ref name="Cavell">J. Anthony Cavell, [http://www.amerisurv.com/PDF/TheAmericanSurveyor_USNationalGrid-Cavell_June2005.pdf USNG: Getting it right the first time]. ''The American Surveyor,'' June 2005.</ref>

==Squares that cross a latitude band boundary==

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*[[Ordnance Survey National Grid]] is another Transverse Mercator system designed for locations in the British Isles

*[[Irish Transverse Mercator]] has replaced the [[Irish grid reference system]]

*[[United States National Grid]] (USNG), developed by the [[Federal Geographic Data Committee]], is an implementation of MGRS for the United States and its possessions.

*[[World Geographic Reference System]] (GEOREF) has been used for air navigation, but is rarely seen today.

*[[Maidenhead Locator System]] is used by amateur radio operators.