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'', is [{{Coor URL}}21_24_35.43062452380_N_157_54_57.89102787040_W_&language=en <code>4Q FJ 1234 6789</code>], which consists of three parts:

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|+ MGRS precision levels

! MGRS Coordinate

! Precision (side length)

|-

| <code>4Q FJ</code>

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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 1a one-meter square precision (10-digit numerical ___location) with spaces permitted only between the 100,000-meter square, the easting, and arethe strippednorthing: ofe.g., spaces<code>4QFJ 12345 67890</code>. The softwaremapping dropsapplication returns a dropped pin representing the [[centroid]] of the 1-meterarea square areareferenced.

==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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===Truncation, not rounding===

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==