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
