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to chart a great circle route by plotting it onto a Mercator Projection and following
short rhumb-line segments as shown in Figure 6.28. The gnomonic projection is used
to find the true great circle and the Mercator to plot the short legs.
Not all azimuthal projections can be visualized as created by projecting a trans-
parent globe by means of a light source. Two important azimuthals are mathematical
projections: the azimuthal equal area and the azimuthal equidistant.
azimuthal equal-area Projection
Since east–west stretching is produced by the failure of meridians to converge pole-
ward on the plane projections, compressing must be introduced to get equivalence.
On
Lambert’s azimuthal equal-area projection (Figure 6.29), this is done by placing
the parallels closer together the farther away they are from the center. Almost the
entire earth can be shown on this projection. Although the azimuthal equal-area pro-
jection cannot be projected with a light source and transparent globe, it is possible to
construct it graphically.
On this projection, azimuths are shown correctly in common with others of the
azimuthal family, but areas can also be compared.
azimuthal equidistant Projection
Another commonly used projection is the azimuthal equidistant, which has parallels
truly spaced along the meridians (Figure 6.30). This projection is most commonly
centered on a place other than the poles to enable one to determine distances from
the center to any other place in the world and to determine the starting azimuths from
those places. Distances between any other places will not be correct; distance can
only be measured from the center point.
fIgURe 6.28.
Great circle routes plotted on the Gnomonic can be approximated with short
rhumb lines on the Mercator.
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