100 THe geOgRaPHiC anD CaRTOgRaPHiC FRaMeWORK
5. Parallels are equally spaced along the meridians (assuming the earth to be a
sphere).
6. Area scale is uniform; that is, 1 square inch of the globe in the high latitudes
and 1 square inch in the low latitudes covers the same earth area.
7. Distance scale is uniform.
Only a globe can combine all these properties because its shape is virtually the
same as the earth’s. When the spherical graticule is transformed onto a plane, which
radically changes its geometry, unavoidable distortions are introduced. Therefore the
only true representation of the earth’s surface geometry is a globe (Figure 6.9).
It must not be assumed, however, that because flat maps have distortions they are
merely poor substitutes for globes or that globes are without disadvantages. Globes
are limited by their practical size. A globe 14 inches in diameter has a scale of 1 inch
to 566 miles, hardly feasible for navigation or showing roads. Globes permit only
one-half of the earth to be seen at a time. Many thematic maps illustrate global pat-
terns; in such cases, it is desirable to view the entire earth at once. A climate map, for
example, is more useful if the entire world pattern can be seen at once and regions
compared. Finally, to show all of the thematic maps in even a small atlas would
require many globes, which would present storage and handling problems.
Projections can be problem-solving tools and should not be considered nega-
tive devices. The distortions of flat maps can be used to advantage. Phenomena that
cannot be shown on a globe can be presented on a flat map by exploiting projec-
tion properties. For example, the gnomonic projection shows all great circle arcs as
straight lines so it can be used for plotting the shortest distance between two points.
The Mercator projection shows loxodromes as straight lines and can be used to plot
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