Mapping Hacks

Find Your Way Around GRASS #69

Chapter 6, Mapping on Your Desktop

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331

HACK

What’s this? Our vector layer of national boundaries got cut off at the edges

of our former region! This is, of course, an interesting lesson in the ways of

GRASS. As it happens, most operations that act on individual layers only do

so within the currently selected region. Sometimes, this is what you want;

many operations in GRASS take a long time to run, and restricting them to

run only within a constrained region of your whole location will make them

run faster, if that’s all you’re interested in. But you should be aware of this

“feature,” as it may cause behavior you’re not expecting when you’re

zoomed in on a small portion of your current location.

So let’s try making that vector map again, but let’s reset our region to the

whole world first:

GRASS:~/gis > g.region rast=nations

GRASS:~/gis > r.to.vect in=nations out=borders feature=area

GRASS:~/gis > d.erase

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

Figure 6-27. Our new borders vector layer