Mapping Hacks

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Chapter 3, Mapping Your World

#31 Plot Dymaxion Maps in Perl

HACK

$map->write( file => "world_cities.png" )

or die $map->errstr;

The script starts by opening a text file called cities.txt and then discards the

header line. Next, it reads the next 50 lines, one by one, splitting each line

up into tab-separated fields, extracting the latitude and longitude from the

second-to-last and last fields on each line, respectively. One important thing

to note is that

Geo::Dymaxion expects latitudes south of the equator and lon-

gitudes west of the prime meridian to be expressed with negative values; this

is taken care of by the two regular expression matches in the main loop. The

latitude and longitude are fed to

Geo::Dymaxion, and the x- and y-coordi-

nates are used to draw a three-pixel-wide red dot on the map in the appro-

priate location. Finally, the updated map is written to a PNG image called

world_cities.png.

Running the Code

In order to run this code, we’ll first need a list of cities. We’ve compiled just

such a list for you, using data from world-gazetteer.com, which you can fetch

from http://mappinghacks.com/data/cities.txt. The file is tab-separated and

contains a bunch of other information, about which we won’t go into detail

here, but that you might find useful for other mapping projects. Next, we’ll

need a Dymaxion map of the world. Dymaxion maps are astonishingly hard

to find on the Internet, ...