Mapping Hacks

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Chapter 6, Mapping on Your Desktop

#69 Find Your Way Around GRASS

HACK

Okay, that’s more like it. Now let’s zoom back in on Western Europe and

redraw our ecology map with the national borders on top:

GRASS:~/gis > d.erase

GRASS:~/gis > g.region Western_Europe

GRASS:~/gis > d.rast eco

GRASS:~/gis > d.vect borders type=boundary color=black

By now, you’ve probably noticed that there’s a scheme

behind the naming of GRASS commands. Commands that

start with

g. are general-purpose, d. commands are display

related,

r. commands work on rasters, v. commands work

on vectors, and so on.

Figure 6-28 shows our revised borders layer drawn in black on top of the eco

layer. You’ll note that the political boundaries and the ecology map don’t

quite match up around the coastlines. Unfortunately, this is simply a side

effect of using very low-resolution sample data—not much we can do about

it here. (Also, you’ll probably notice that these boundaries date to before

1990, but that’s beside the point).

Now that we’ve made this informative and attractive map, what if we want

to get back to it later? Fortunately, GRASS provides the d.save command,

which generates a shell script of the commands used to generate the current

view in our monitor. Run

d.save -c > europe.sh and examine the contents

of europe.sh:

# Shell Script created by d.save Sun Jun 27 18:16:20 2004

d.erase

g.region n=60:04:48N s=36:43:12N e=18:48E w=13:07:12W nsres=0:04:48 ...