World Geographic Reference System: Difference between revisions

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{{for|the bibliographic database about the geosciences|GeoRef}}

{{Refimprove|date=September 2012}}

{{short description|Grid-based method of specifying locations}}

The '''worldWorld geographicGeographic referenceReference systemSystem''' ('''GEOREF''') is a [[geocode]], a grid-based method of specifying locations on the surface of the [[Earth]]. GEOREF is essentially based on the geographic system of [[latitude]] and [[longitude]], but using a simpler and more flexible [[notation]]. GEOREF was used primarily in [[aeronautical chart]]s for [[air navigation]],<ref>{{cite report |author=DMA |author-link=Defense Mapping Agency |date=20 September 1990 |title=Defense Mapping Agency Technical Manual |series=TM 8358.1 |chapter=Chapter 5: Geographic Coordinate References |chapter-url=http://earth-info.nga.mil/GandG/publications/tm8358.1/tr83581c.html#ZZ38 |access-date=2016-12-16}}</ref> particularly in military or inter-service applications, but it is rarely seen today.{{cn|date=October 2020}} However, GEOREF can be used with any map or chart that has latitude and longitude printed on it.

== Quadrangles ==

The '''world geographic reference system''' ('''GEOREF''') is a grid-based method of specifying locations on the surface of the [[Earth]]. GEOREF is essentially based on the geographic system of [[latitude]] and [[longitude]], but using a simpler and more flexible [[notation]]. GEOREF was used primarily for [[air navigation]], particularly in military or inter-service applications, but it is rarely seen today. However, GEOREF can be used with any map or chart that has latitude and longitude printed on it.

== Operation ==

GEOREF is based on the standard system of [[latitude]] and [[longitude]], but uses a simpler and more concise notation. GEOREF divides the Earth's surface into successively smaller quadrangles, with a notation system used to identify each quadrangle within its parent. Unlike latitude/longitude, GEOREF runs in one direction horizontally, east from the 180° [[meridian (geography)|meridian]]; and one direction vertically, north from the [[South Pole]]. GEOREF can easily be adapted to give co-ordinates with varying degrees of precision, using a 2–12 character [[geocode]].

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GEOREF co-ordinates are defined by successive divisions of the Earth's surface, as follows:

* The first level of GEOREF divides the world into quadrangles each measuring 15 degrees of longitude by 15 degrees of latitude; this results in 24 '''zones''' of longitude and 12 '''bands''' of latitude. A longitude zone is identified by a letter from A to Z (omitting I and O) starting at 180 degrees and progressing eastward through the full 360 degrees of longitude; a latitude band is identified by a letter from A through M (omitting I) northward from the south pole. Hence, any 15 degree quadrangle can be identified by two letters; the easting (longitude) is given first, followed by the northing (latitude). These two letters are the first two characters of a full GEOREF coordinate.

* Each 15-degree quadrangle is further divided into smaller quadrangles, measuring 1 degree of longitude by 1 degree of latitude. These quadrangles are lettered A to Q (omitting I and O), running from west to east for longitude; and A to Q (omitting I and O), running south to north for latitude. These letters form the third and fourth characters of a full GEOREF coordinate. Four letters thus identify any 1-degree quadrangle in the world.

* Each of the 1-degree quadrangles is further subdivided into 60 1-minute longitude zones, numbered 00 through 59 from west to east, and 60 1-minute latitude bands, numbered 00 to 59 from south to north. These numbers are always written as two digits, with a leading zero if necessary, and the easting is always followed by the northing. Thus, 4 letters and 4 digits give the position of any 1-minute quadrangle.

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[[Image:georef-local.jpg|thumb|256px|right|The GJ local grid]]

For example, on a GEOREF chart, [[Naval Air Station Patuxent River]] (38°17′10″N 76°24′42″W) / (38.286108, -76.4291704) is located (to the nearest minute) at position GJPJ3716GJPJ3417. <!-- Figure needed! In figure 12-10, the blacked-out square (PJ) within the enlarged 15° square (GJ) indicates the 1° area that contains Patuxent. -->

[[Image:Georef Example Patuxent.png|Breakdown of Georef co-ordinate GJPJ3716 into 15-degree quadrangle (GJ), 1-degree quadrangle (PJ), minutes east (3734), and minutes north (1617).]]

To locate the position from the coordinates, proceed as follows:

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* Right in zone GJ to the lettered 1° column P

* Up in zone GJ to the lettered 1° row J

* Right in the 1° horizontal zone to 3734 minutes

* Up in the 1° vertical zone to 1617 minutes

The same co-ordinate shown in 6-digit (1/10 minute) format is GJPJ370160GJPJ342171 and in 8-digit (1/100 minute) format is GJPJ37001600GJPJ34241716.

== Designation of area ==

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== See also ==

*[[List of geodesic-geocoding systems]]

* [[Global Area Reference System]] (GARS)

* [[Maximum elevation figure]] correlated to each GEOREF quadrangle on [[visual flight rules|VFR]] aviation maps

* [[Military Grid Reference System]] (MGRS)

* [[Lowest safe altitude#Area minimum altitudes|Area minimum altitudes]] on [[instrument flight rules|IFR]] charts

== References ==

{{Reflist}}

* [http://www.map-reading.com/ch4-4.php GEOREF info] from map-reading.com

* [http://earth-info.nga.mil/GandG/coordsys/grids/georef.pdf World Geographic Reference System (GEOREF)], National Geospatial-Intelligence Agency

* [http://www.colorado.edu/geography/gcraft/notes/coordsys/coordsys.html ''Coordinate Systems Overview''], from the University of Colorado

{{Geocoding-systems}}

[[Category:Geocodes]]

[[Category:Geographic coordinate systems]]

[[Category:Military cartography]]