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 pointsrather defines a square grid area on the earthEarth'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 Polar Stereographic coordinate system|universalUniversal polarPolar stereographicStereographic]] (UPS)]] grid system,systems butand usesis aused differentas labelinga convention. The MGRS is used[[geocode]] for the entire earthEarth.

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)

* 12345678<code>1234 6789</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 is a point reference system. When the term 'grid square' is used, it can refer to a square with a side length of {{convert|10|km|mi|0|abbr=on}}, 1&nbsp;km, {{convert|100|m|ft|0|abbr=on}}, 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.) 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. 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.

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" may be a better descriptor of such areas.)

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

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

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

* 4QFJ 1 6 ...............precision level 10&nbsp;km

*|+ 4QFJMGRS 12 67 .............precision levellevels 1&nbsp;km

! MGRS Coordinate

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

! Precision (side length)

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

|-

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

| <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 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 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.

==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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For the row letters, there are actually two alternative lettering schemes within MGRS:

* In the ''AA scheme'',<ref name="MGRS_Final_Guidance">

[http://earth-info.nga.mil/GandG/coordsys/MGRS_Final_Guidance.doc NGA Guidance for the Military Grid Reference System (MGRS).]</ref> also known as ''MGRS-New'',<ref name="Military_Map_Reading_201">[{{cite web|url=http://earth-info.nga.mil/GandG/coordsys/mmr201.pdf |title=Military Map Reading 201]|archive-url=https://web.archive.org/web/20210224185834/earth-info.nga.mil/GandG/coordsys/mmr201.pdf|archive-date=February 24, 2021}}, published by [[National Geospatial-Intelligence Agency|NGA]]</ref> which is used for [[WGS84]] and some other modern [[datum (geodesy)|geodetic datum]]s, the letter for the first row – just north of the equator – is A in odd-numbered zones, and F in even-numbered zones, as shown in figure 1. Note that the westmost square in this row, in zone 1, has identification AA.

* In the alternative ''AL scheme'',<ref name="MGRS_Final_Guidance"/> also known as ''MGRS-Old'',<ref name="Military_Map_Reading_201"/> which is used for some older [[datum (geodesy)|geodetic datum]]s, the row letters are shifted 10 steps in the alphabet. This means that the letter for the first row is L in odd-numbered zones and R in even-numbered zones. The westmost square in the first row, in zone 1, has identification AL.

If an MGRS coordinate is complete (with both a grid zone designation and a 100,000 meter square identification), and is valid in one lettering scheme, then it is usually invalid in the other scheme, which will have no such 100,000 meter square in the grid zone. (Latitude band X is the exception to this rule.) Therefore, a position reported in a modern [[datum (geodesy)|datum]] usually can notcannot be misunderstood as using an old datum, and vice versa – provided the datums use different MGRS lettering schemes.

In the map (figure 1), which uses the AA scheme, we see that Honolulu is in grid zone 4Q, and square FJ. To give the position of Honolulu with 100&nbsp;km resolution, we write 4QFJ.

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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".

===TruncateTruncation, don'tnot roundrounding===

As mentioned above, when converting UTM coordinates to an MGRS grid reference, or when abbreviating an MGRS grid reference to lower precision, onecoordinates shouldare ''truncate''{{em|truncated}}, and not rounded up (which would indicate the coordinates,next notadjacent grid square instead of the surrounding roundsquare).

This haswas beenonce controversial in the past, sinceas 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.

*A modification of the Military Grid Reference System is used by the [https://www.luomus.fi/en/grids-mapping-atlas-florae-europaeae Atlas Florae Europaeae] for mapping the distribution of [[vascular plants]] in Europe.

*[[Natural Area Code]]

*[https://deeppradhan.heliohost.org/gis/indian-grid/ Indian Grid System] is a [[Lambert Conformal Conic]] based Grid Reference System used in [[India]] and neighbouring countries.

==References==

{{Citations broken|section|date=March 2022}}

{{reflist}}

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*[http://www.colorado.edu/geography/gcraft/notes/coordsys/coordsys_f.html A list of coordinate systems] – by Prof. Peter H. Dana at the Univ. of Colorado

*[http://earth-info.nga.mil/GandG/coordsys/grids/referencesys.html Grids and Reference Systems], by [[National Geospatial-Intelligence Agency|NGA]].

* [https://geographiclib.sourceforge.io GeographicLib] provides a utility GeoConvert (with source code) for conversions between geographic, [[Universal Transverse Mercator|UTM]], [[Universal Polar Stereographic|UPS]], and MGRS. Here is an [https://geographiclib.sourceforge.io/cgi-bin/GeoConvert online version of GeoConvert].

* [https://www.gridscout.net/ GridScout], a command-line tool for querying the [[Google Maps API]] and displaying results in MGRS coordinates.

* Army Study Guide: [http://www.armystudyguide.com/content/Prep_For_Basic_Training/Prep_for_basic_land_navigation/locate-a-point-using-the-.shtml Locate a point using the US Army Military Grid Reference System (MGRS)]

* [http://www.maps.pixelis.es/ Web application to locate GPS coordinates in MGRS, UTM, DMS and decimal format] {{es icon}}

* [http://www.mappingsupport.com/p/gmap4.php?usng=4QFJ12345678&z=7&t=t1 Gmap4], an enhanced Google map viewer with a MGRS grid and more.

{{-}}

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[[Category:Military cartography]]

[[Category:Geodesy]]

[[Category:Geocodes]]