Universal Transverse Mercator Military Grid

meridians as does the track of a vessel under a true course. On the globe the parallels become shorter toward the poles, and their length is proportionate to the cosine of latitude. In the Mercator projection the parallels are equally long. This means that any parallel is increased by 1/cos q, or sec q, where q is the latitude in degrees. To have the same scale along the parallels as along the meridians, you must increase each degree of latitude by the secant of the latitude. In this math- ematical transformation, the tangent cylinder concept was not employed, nor is it ever employed, in the Mercator projection. A Mercator projection table is used to plot the meridional distances. For intensive study on elements of map projection, you may refer to special publications published by the U.S. Coast and Geodetic Survey that deal with this subject. Universal Transverse Mercator Military Grid An extensive application of the transverse Mercator projection is in a grid reference system for military maps called the universal transverse Mercator (UTM) military grid system. In this system a reference plane grid, like those used in our state grid systems, is imposed on transverse Mercator projections of relatively small areas. The basic Figure 9-14.—(A) Grid zone designations of the military grid reference system; (B) 100,000-meter-square designations in the UTM military grid system, 9-13