Mapping Hacks

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Chapter 6, Mapping on Your Desktop

#72 Add Relief to Your Topographic Maps

HACK

few configurable settings that good software design dictates should be

turned into command-line options, rather than source code constants. Of

course, if we solved all of these remaining issues, we might find ourselves

with something a lot closer to a software product than a simple hack!

HACK

#72

Add Relief to Your Topographic Maps Hack #72

Using GRASS and some digital elevation models, you can give existing topo

maps a more expressive “3-D” look.

Topographic maps can be a useful tool for getting a sense of the lay of the

land, but the contour lines used to express topographic variation can be a

little hard to get one’s head around at a glance. Does that path lead uphill or

downhill? By adding shadows to the map that correspond to the contours of

the land (as if the sun were overhead), we can create the impression of relief

on our topo maps, making it easier for the eye to pick out hills and valleys.

This technique is called hill shading, and GRASS offers several tools for add-

ing hill shading to a topographic map.

Getting the Data

For simplicity—and because there is a wealth of freely available data for the

region—we’ll try our hand at adding hill shading to a topographic map of

San Francisco. Hill shading involves not only a nice topo map, but also ele-

vation data to plot the relief with. Fortunately, the USGS Bay ...