a transverse Mercator projection, the cylinder is ro-tated 90 degrees from this position to bring it tangentto a meridian. Figure 9-13 shows the appearance of themeridians and parallels on the transverse Mercatorworld projection when the cylinder is flattened out.In this case, the cylinder was placed tangent to themeridian running through 0-degrees and 180-degreeslongitude.You can see that, in general, a transverse Mercatorprojection has less distortion than a Mercator pro-jection does. You also can see that, unlike distortionon a Mercator projection, distortion on a transverseMercator increases with longitude as well as withlatitude away from the meridian of tangency. This isindicated by the shaded areas shown in figure 9-13.they lie in the same latitude, they would have thesame size on a Mercator projection. On the transverseMercator projection, however, the area in the higherlongitude would be larger.The important thing to note about the transverseMercator, however, is the fact that in any given areathe distortion is about the same in all directions. It isthis fact that makes the transverse Mercator the mostfeasible projection for use with the military grid ref-erence system.A rhumb line is a curve on the surface of asphere that cuts all meridians at the same angle. Amathematical navigational device, developed to plotthe Mercator-projected maps, makes the rhumb linea straight line on the chart, thus preserving theThese areas are the same size on the ground. Sincesame angle of bearing with respect to the intersectedFigure 9-13.—Meridians and parallels on a transverse Mercator projection.9-12
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