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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
An example of an ''MGRS coordinate'', or ''grid reference'',
* <code>4Q</code> (grid zone designator, GZD)
* <code>FJ</code> (the 100,000-meter square identifier)
*
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 or polygon on the Earth with a side length of 10 km, 1 km, 100 m, 10 m or 1 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.)
{| class="wikitable" style="text-align: left;"
! 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 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">
* 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
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 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".
===
As mentioned above, when converting UTM coordinates to an MGRS grid reference, or when abbreviating an MGRS grid reference to lower precision,
This However, truncation
Likewise, the civilian/continental version of MGRS, [[USNG]], ==Squares that cross a latitude band boundary==
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But an MGRS grid reference can denote an area that crosses a latitude band boundary. For example, when describing the entire square BT, should it be called 1PBT or 1QBT? Or when describing the 1000-meter square BT8569, should it be called 1PBT8569 or 1QBT8569? In these cases, software that interprets an MGRS grid reference should accept both of the possible latitude band letters. A practical motivation was given in the release notes for GEOTRANS,<ref name="Geotrans"/> Release 2.0.2, 1999:
<blockquote>The MGRS module was changed
==Polar regions==
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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.
*[[Natural Area Code]]
==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]].
* 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)]
{{-}}
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[[Category:Military cartography]]
[[Category:Geodesy]]
[[Category:Geocodes]]
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