Mapping Hacks

Experiment with Different Cartographic Projections #28

Chapter 3, Mapping Your World

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HACK

The first command generates the Lambert’s projection in gray, using the -K

command to tell pscoast to leave out the PostScript footers that indicate that

the document is finished. The second command appends an Albers Equal-

Area projection to the PostScript file using the

-JB option, which utilizes the

same projection parameters. The

-O command tells pscoast to omit the Post-

Script headers from the second map, which will cause the second map to

simply be drawn on top of the first. The

-K and -O commands can be com-

bined to successively overlay three or more layers of output from GMT.

Pseudocylindrical Projections

Some projections have a mathematical, rather than geometric, origin. The

sinusoidal projection, for example, plots straight parallels against meridians

that are curved relative to the cosine of the longitude. Imagine what you might

get if you smoothed the ends of the cylinder to a point before attempting a

Mercator projection, and you have the basic idea, which is why the sinusoidal

projection is sometimes referred to as a pseudocylindrical projection. The result

is shown in Figure 3-26, which we generated using the

-JI option to pscoast.

Although the sinusoidal projection distorts shapes rather badly away from

the equator, it preserves land area, and it has the advantage of being nearly

as easy