Mapping Hacks

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Chapter 3, Mapping Your World

#29 Plot Arbitrary Points on a World Map

HACK

“Experiment with Different Cartographic Projections” [Hack #28]. Some-

times, the best projection, however, is no projection at all. The Equidistant

Cylindrical projection is made by treating every degree of latitude and

longitude as equal in length, resulting in a perfectly rectangular map with a

2:1 width-to-height ratio. First attributed to Eratosthenes of Cyrene in the

third century BC, this projection does not preserve area, shape, direction,

distance, or scale (except along meridians), but it has one supreme advan-

tage. It’s easy to hack!

Here’s why: since meridians and parallels in this projection meet at equally

spaced right angles, latitude and longitude can simply be treated as rectan-

gular coordinates, shortcutting the tortuous spherical trigonometry that usu-

ally plagues the art of cartographic projection. By consequence, the

Equidistant Cylindrical projection is also referred to as equirectangular,or

simply rectangular. (You’ll also see it referred to as the Plate Carrée projec-

tion, which is French for “square plane.”) Naturally, some cartographers

think it’s cheating to simply set x=Rλ and y=Rφ, and so maps of this kind

are also referred to as unprojected.

Finding Base Maps on the Web

Because the Equidistant Cylindrical projection is so hackable, lots of inter-

esting mapping apps like xplanet

[Hack