Global Positioning System Reference
In-Depth Information
FIGURE 4.9.
Mercator's projection, from 80
\
north to 80
\
south. Area is distorted,
particularly near the poles, but loxodromes are straight lines on this map. Great-
circle routes are complicated, however. This illustration shows three great-circle
routes marking the shortest distance routes between Wellington in New Zealand and
Cape Town in South Africa, between London and Los Angeles, and between Tokyo
and São Paulo.
tor projection (except for the so-called
oblique
variant), and meridians are
always perpendicular to parallels. Another benefit of Mercator maps is that
they are conformal, so that locally, the maps accurately reproduce shapes,
distances, and angles. Thus, for example, while Greenland is represented
as far too big, its shape is not much distorted. The Mercator projection also
works well for equatorial maps (because the projection cylinder is tangen-
tial to the globe at the equator).
There is no such thing as a free lunch, however. Mercator distorts areas
and distances, more so farther away from the equator and horribly so near
the poles, as you can see in figure 4.9. (Recall that South America is more
than eight times bigger than Greenland.) Not only that, but great circles
are also complicated—far from the convenient straight lines of, for exam-
ple, gnomonic projections. In figure 4.9 we see three great circle routes
(that is, shortest routes) between distant cities. As you can see from this fig-
ure, the Mercator projection will not easily get you from
A
to
B
in the short-
