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Figure 9.7 Goode's Homolosine Projection. Source: NASA, Pseudocylindrical Projections.
Pseudocylindrical_Projections.html
9.7 Contemporary approach: Web Mercator Auxiliary Sphere projection
Many contemporary mapping packages employ a simple grid transfer from
a sphere to a plane to portray the graticule and the attached landmasses.
Naturally, distortion is severe; what is valuable is that this particular charac-
terization is easily projected into existing projections. When one begins with
a base, such as the Robinson projection, that ease of reprojection is lost as
numerical truncation of infinitely repeating decimals may cause a “rupture” in
the reprojection process forcing a crash of hardware.
As times change, so do different needs for projections. In the contemporary
world of online mapping, the Web Mercator Auxiliary Sphere projection has
become the default projection of Google Maps, Google Earth, ArcGIS Online,
and no doubt other related services already online or yet to come. This projec-
tion is a Mercator-like projection that treats the two-dimensional curved surface
being projected as that of an oblate spheroid rather than as that of a sphere. Its
advantage is straightforward—most major online mapping tools use this projec-
tion. Therefore, thematic data from one mapping platform, such as world ecore-
gions or ocean currents, can be easily moved to another mapping platform. Its
disadvantages are also straightforward; it is a Mercator projection and has the
same limitations.
Alistair Aitchison (2011) offered an interesting example, in terms of maps of
Great Britain, of the differences that come from using a web Mercator projection
based on a spherical surface and one using an oblate spheroidal surface. The
differences are small, but discernible. When the sphere's polar axis is squashed,
the landmasses on the surface are pushed more toward the Equator than when
it is not. Issues involving large scale mapping and projections may play out in
related, but not identical, ways in association with shape choice of the underly-
ing projection surface—the differences may or may not be discernible.
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