Thursday, 24 March 2011

True size of Africa

The traditional Mercator map, which dates from around 1569, is accurate regarding shape instead of size. A mapmaker cannot accurately represent both — if you want an accurate shape for land masses, you have to sacrifice proportionality, i.e., the relative sizes will be distorted. Moreover, the distortion increases as you move away from the equator, becoming severe near the poles. This leads to what is known as "the Greenland Problem." Greenland appears to be the same size as Africa, yet the land mass of Africa is actually 14 times larger:

Gerardus Mercator, 1569
Cyllindrical Conformal[Lambert Conformal Conic with standard parallels at or equidistant from the equator]
Conformal: local angles are preserved, and local circles are not deformed — at every point east/west scale is the same as north/south scaleDistortion is constant along any parallel, and any parallel can be defined as standardConstant bearings (rhumb lines / loxodromes) are straight linesMap extends infinitely North and South
Google Maps (note the dynamic scale bar)[navigating a constant bearing]

Gall-Peters(in ArcMap, use Cyllindrical Equal-Area)
James Gall, 1855Arno Peters, 1967 (presented 1973)
Gall OrthographicPeters[Cyllindrical Equal Area with standard parallels at 45° N/S]
UNESCONATOVaticanWorld Council of Churches

Winkel Tripel
Oswald Winkel, 1921
standard parallels of component Equirectangular at ~50° 27' 35" N/S
[mathematical average of Equirectangular and Aitoff]
Pleasant balance of shape and scale distortionUnlike other Winkel projections, there are no standard parallels on the final mapNo point is distortion-free
The Times AtlasNational Geographic (since 1998)

No comments:

Post a Comment