Mapping Hacks

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Chapter 3, Mapping Your World

#30 Plot a Great Circle on a Flat Map

HACK

to the cosine of the latitude, as would be depicted on a globe. Instead of

using the following code to determine the x-coordinate:

my $x = ($lon - $left) * $x_scale;

we could use this calculation to plot a sinusoidal projection of our data:

my $x = ($lon - $left) * $x_scale * cos( $lat );

Although this distorts the shapes of large areas, it’s easy to calculate, and it

preserves the relationship of latitude and longitude better at temperate lati-

tudes. For this reason, the TIGER Map Server makes use of the sinusoidal

projection, as discussed in “Make Free Maps of the United States Online”

[Hack #14].

We examine still other cartographic projections in “Experiment with Differ-

ent Cartographic Projections”

[Hack #28]. Still, no other projection beats the

Equidistant Cylindrical projection for ease of use, and there’s absolutely

something to be said for that.

See Also

• “View Your Photo Thumbnails on a Flash Map” [Hack #39]

• “Experiment with Different Cartographic Projections” [Hack #28]

• “Make Free Maps of the United States Online” [Hack #14]

• “Plot Points on an Interactive Map Using DHTML” [Hack #41]

• http://flatplanet.sourceforge.net/maps/

• http://mappinghacks.com/maps/

HACK

#30

Plot a Great Circle on a Flat Map Hack #30

Wherein our heroes discover that the shortest distance between two points

on a globe is not a straight ...