World Geographic Reference System: Difference between revisions

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

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

'''Georef'''The ('''World Geographic Reference System''' ('''GEOREF''') is a [[geocode]], a grid-based method of specifying locations on the surface of the [[Earth]]. GeorefGEOREF is essentially based on the geographic system of [[latitude]] and [[longitude]], but using a simpler and more flexible [[notation]]. GeorefGEOREF 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, GeorefGEOREF can be used with any map or chart that has latitude and longitude printed on it.

== Quadrangles ==

'''Georef''' ('''World Geographic Reference System''') 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.

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

== Operation ==

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

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]].

* The first level of GeorefGEOREF 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 GeorefGEOREF coordinate.

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

* 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 GeorefGEOREF coordinate. Four letters thus identify any 1-degree quadrangle in the world.

* 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.

* Each of the 1-minute quadrangles may be further divided into 10 or 100 smaller divisions both north–south and east–west, permitting the identification of 0.1-minute or 0.01-minute quadrangles. The GeorefGEOREF coordinate for any 0.1-minute quadrangle consists of four letters and six numbers; the GeorefGEOREF coordinate for any 0.01-minute quadrangle consists of four letters and eight numbers.

The initial two letters of a GeorefGEOREF reference, designating the 15 degree quadrangle, can be omitted, if it is clear which 15 degree quadrangle the reference applies to (e.g., when working within a restricted geographical area).

=== Example ===

[[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:

Line 30:

* 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 ==

Extensions to the above notation allow the GeorefGEOREF system to be used to designate an area around a reference point. This is achieved by adding an area designation to a base GeorefGEOREF co-ordinate. The area designation can be the letter S, to specify the sides of a rectangle (separated by the letter X); or the letter R, to specify the radius of a circle. In both cases the units are nautical miles. In addition, the letter H can be added, followed by an altitude in thousands of feet.

For example, the reference GJQJ0207S6X8 designates a rectangle centered on Deal Island (GJQJ0207), running {{convert|6|nmi|km|0}} east–west and {{convert|8|nmi|km|0}} north–south. Designation GJPJ4103R5 means a circle around Point Lookout (GJPJ4103) with a radius of {{convert|5|nmi|km|0}}. Designation GJPJ3716H17 means a height of 17,000 feet over GJPJ3716.

== See also ==

*[[List of geodesic-geocoding systems]]

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

* [[Maximum elevation figure]] correlated to each GeorefGEOREF 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://www.tpubmap-reading.com/content/combat/14308/css/14308_234ch4-4.htmphp U.S.GEOREF Navy Operations Specialist manualinfo], from Integrated Publishingmap-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]]