The World Geographic Reference System (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 charts 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.
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; 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.
GEOREF co-ordinates are defined by successive divisions of the Earth's surface, as follows:
The initial two letters of a GEOREF 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).
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 GJPJ3417.
To locate the position from the coordinates, proceed as follows:
The same co-ordinate shown in 6-digit (1/10 minute) format is GJPJ342171 and in 8-digit (1/100 minute) format is GJPJ34241716.
Extensions to the above notation allow the GEOREF system to be used to designate an area around a reference point. This is achieved by adding an area designation to a base GEOREF 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 6 nautical miles (11 km) east–west and 8 nautical miles (15 km) north–south. Designation GJPJ4103R5 means a circle around Point Lookout (GJPJ4103) with a radius of 5 nautical miles (9 km). Designation GJPJ3716H17 means a height of 17,000 feet over GJPJ3716.