Grids - Grid Reference Box


4­7. GRID REFERENCE BOX
A grid reference box appears in the marginal information of each map sheet. It contains step­by-step instructions for using the grid and the US Army military grid reference system. The grid reference box is divided into two parts.


a. The left portion identifies the grid zone designation and the 100,000­meter square. If the sheet falls in more than one 100,000­meter square, the grid lines that separate the squares are shown in the diagram and the letters identifying the 100,000­meter squares are given.


EXAMPLE: On the Columbus map sheet, the vertical line labeled 00 is the grid line that separates the two 100,000­meter squares, FL and GL. The left portion also shows a sample for the 1,000­meter square with its respective labeled grid coordinate numbers and a sample point within the 1,000­meter square.

b. The right portion of the grid reference box explains how to use the grid and is keyed on the sample 1,000­meter square of the left side. The following is an example of the military grid reference:

EXAMPLE: 16S locates the 6° by 8° area (grid zone designation).
4­8. OTHER GRID SYSTEMS

The military grid reference system is not universally used. You must be prepared to interpret and use other grid systems, depending on your area of operations or the personnel you are operating with.

a. British Grids. In a few areas of the world, British grids are still shown on military maps. However, the British grid systems are being phased out. Eventually all military mapping will be converted to the UTM grid.

b. The World Geographic Reference System (GEOREF). This is a worldwide position reference system used primarily by the US Air Force. It may be used with any map or chart that has latitude and longitude printed on it. Instructions for using GEOREF data are printed in blue and are found in the margin of aeronautical charts. This system is based upon a division of the earth's surface into quadrangles of latitude and longitude having a systematic identification code. It is a method of expressing latitude and longitude in a form suitable for rapid reporting and plotting. The GEOREF system uses an identification code that has three main divisions.

(1) First division. There are 24 north­south (longitudinal) zones, each 15° wide. These zones, starting at 180° and progressing eastward, are lettered A through Z (omitting I and O). The first letter of any GEOREF coordinate identifies the north­south zone in which the point is located. There are 12 east­west (latitudinal) bands, each 15° wide. These bands are lettered A through M (omitting I) northward from the south pole. The second letter of any GEOREF coordinate identifies the east­west band in which the point is located. The zones and bands divide the earth's surface into 288 quadrangles, each identified by two letters.
(2) Second division. Each 15° quadrangle is further divided into 225 quadrangles of 1° each (15° by 15°). This division is effected by dividing a basic 15° quadrangle into 15 north-south zones and 15 east­west bands. The north­south zones are lettered A through Q (omitting I and O) from west to east. The third letter of any GEOREF coordinate identifies the 1° north­south zone within a 15° quadrangle. The east­west bands are lettered A through Q (I and O omitted) from south to north. The fourth letter of a GEOREF coordinate identifies the 1° east­west band within a 15° quadrangle. Four letters will identify any 1° quadrangle in the world.

(3) Third division. Each of the 1° quadrangles is divided into 3,600 one­minute quadrangles. These one minute quadrangles are formed by dividing the 1° quadrangles into 60 one­minute north­south zones numbered 0 through 59 from west to east, and 60 east-west bands numbered 0 to 59 from south to north. To designate any one of the 3,600 one­minute quadrangles requires four letters and four numbers. The rule READ RIGHT AND UP is always followed. Numbers 1 through 9 are written as 01, 02, and so forth. Each of the 1­minute quadrangles may be further divided into 10 smaller divisions both north­south and east­west, permitting the identification of 0.1­minute quadrangles. The GEOREF coordinate for any 0.1­minute quadrangle consists of four letters and six numbers.