Starting at the 180th meridian and progressingeastward by the compass, the earth’s surface is dividedinto a succession of north-south zones, eachextending for 6 degrees of longitude. These zones arenumbered from 1 through 60. Between latitude 80°Sand 84°N, each zone is divided into a succession ofeast-west rows, each containing 8 degrees of latitude,with the exception of the northernmost row, whichcontains 12 degrees of latitude. Rows are designatedby the letters C through X, with the letters I and Oomitted. The lettering system begins at thesouthernmost row and proceeds north. For a particularzone-row area, the designation consists of first, thezone number and next, the row letter, such as 16S,which means row S in zone 16.The polar regions (that is, the areas above 84°Nand below 80°S) have only two zones in each area.These lie on either side of the 0-degrees and 180-degrees meridian. In the North Polar region, the halfof the region that contains the west longitudes is zoneY; that containing the east longitudes is zone Z. Nonumbers are used with these designations. Similarly,in the South Polar region, the half containing the westlongitudes is zone A; that containing the eastlongitudes, zone B.In the UTM Military Grid System, a particularpoint on the earth is further identified by the 100,000-meter square in which it happens to lie. Each of the6-degree longitude by 8-degree latitude zone-rowareas in the system is subdivided into squaresmeasuring 100,000 meters on each side. Each north-south column of 100,000-meter squares is identifiedby letter as follows. Beginning at the 180th meridianand proceeding eastward, you will find six columns offull squares in each 6-degree zone. Besides the fullcolumns, usually partial columns also run along thezone meridians. The partial columns and full columnsin the first three zones are lettered from A through Z,again with the letters I and O omitted. In the next timezones, the lettering systems begins over again.Observe, for example, figure 9-14, view B. Thisfigure shows the zone-row areas in 1N, 2N, and 3N,and 1P, 2P, and 3P. The zone meridians shown are180°W, 174°W, 168°W, and 162°W; the zone-rowparallels shown are the equator (0° latitude), 8°N, and16°N. The first 100,000-meter-square column to theeast of 180 degrees is the partial column A. Nextcomes six full columns: B, C, D, E, F, and G. Thencomes partial column H, to the west of the zonemeridian 174°W. The first column to the east of zonemeridian 174°W is partial column J; then comes thefull-size columns K, L, M, N, P, and Q, followed bypartial column R. To the east of zone meridian 168°W,the first column is partial column S; then comes thesix full columns T, U, V, W, X, and Y, and the partialcolumn Z to the west of zone meridian 162°W.The east-west rows of 100,000-meter squares aredesignated by the letters A through V, again with I andO omitted. For columns in the odd-numbered zones,the first row of squares north of the equator has theletter designation A; for columns in the even-numbered zones, the first row of squares north of theequator has the letter designation F. Rows above andbelow this row are designated alphabetically. The firstrow south of the equator in the odd-numbered zones,for example, has the letter designation V, while thefirst row south of the equator in the even-numberedzones has the letter designation E.The complete designation for a particular100,000-meter square consists of the number-letter,zone-row designation plus the two-letter, 100,000-meter-square designation. For example, thedesignation 1NBA means the first full square east ofthe 180th meridian and north of the equator (squareBA) in zone-row 1N, as shown in figure 9-14, view B.If you know the latitude and longitude of a certainpoint on the earth, you can determine the designationof the 100,000-meter square in which the point lies.Take Fort Knox, Kentucky, for example, which liesapproximately at latitude longitudeYou will find this latitude and longitude infigure 9-15. The point lies in column 16, row S, and100,000-meter square ES; therefore, the 100,000-meter-square designation for Fort Knox, Kentucky, is16SES.The location of a particular point within a100,000-meter square is given by naming the gridcoordinates of the 100-meter square (or, for moreprecise location, of the 10-meter square) in which thepoint lies. Within each zone the point of origin formeasuring these coordinates is the point ofintersection between the zone central meridian andthe equator. A false easting of 500,000 meters, insteadof a value of O meters, is assigned to the centralmeridian to avoid the use of west or negative east-westcoordinates. For points in the earth’s SouthernHemisphere, the equator is assigned a false northingof 10,000,000 meters to avoid the use of south ornegative north-south coordinates, and northing valuesdecrease from the equator toward the South Pole. Forpoints in the Northern Hemisphere, the equator has acoordinate value of 0 meters, and northing valuesincrease toward the North Pole.This procedure results in very large coordinatevalues when the coordinates are referenced to the9-14
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