Calculating Polygon Areas in GRASS GIS
While playing around with the ever useful GRASS GIS, it occured to me that I often do all of my ‘simple’ tasks in QGIS and only break out GRASS for the heavy analysis. This means that I don’t always know how to do some basic tasks using GRASS directly. This became apparently while trying to calculate areas on a polygon layer using GRASS. It turns out that it’s a simple task, once you know how, but—as with most things GRASS—can be a bit tricky at first. So, how do we do it?
Basically, the idea is to create a new column where the area data will live:
v.db.addcol mapname col=”area_sqkm DOUBLE PRECISION”
Then we’ll fill the new column with the area using v.to.db. Note that v.to.db will also let you calculate a lot more than just the area; see the full list.
v.to.db map=mapname option=area col=area_sqkm unit=k
Other options for units are:
- Mi: miles
- F: feet
- Me: meters
- K: kilometers
- A: acres
- H: hectares
- R: radians
- D: degrees
Posted: November 28th, 2012 under GIS.