Transverse Mercator Projection

a transverse Mercator projection, the cylinder is ro- tated 90 degrees from this position to bring it tangent to a meridian. Figure 9-13 shows the appearance of the meridians and parallels on the transverse Mercator world projection when the cylinder is flattened out. In this case, the cylinder was placed tangent to the meridian running through 0-degrees and 180-degrees longitude. You can see that, in general, a transverse Mercator projection has less distortion than a Mercator pro- jection does. You also can see that, unlike distortion on a Mercator projection, distortion on a transverse Mercator increases with longitude as well as with latitude away from the meridian of tangency. This is indicated by the shaded areas shown in figure 9-13. they lie in the same latitude, they would have the same size on a Mercator projection. On the transverse Mercator projection, however, the area in the higher longitude would be larger. The important thing to note about the transverse Mercator, however, is the fact that in any given area the distortion is about the same in all directions. It is this fact that makes the transverse Mercator the most feasible projection for use with the military grid ref- erence system. A rhumb line is a curve on the surface of a sphere that cuts all meridians at the same angle. A mathematical navigational device, developed to plot the Mercator-projected maps, makes the rhumb line a straight line on the chart, thus preserving the These areas are the same size on the ground. Since same angle of bearing with respect to the intersected Figure 9-13.—Meridians and parallels on a transverse Mercator projection. 9-12