r.slope.aspect
module.Convert the vector map to raster with the command:
v.to.rast input=edifici output=edifici.mask use=val layer=1 value=1 rows=4096
Remember that this conversion is run following the region settings. You can view the region settings with:
g.region -p
Now the resulting raster map becomes our MASK
:
r.mask input=edifici.mask maskcats=*
From now on, all subsequent operations will be limited to the cells defined in our MASK
, corresponding to built
areas or settlements.
If you need to remove the MASK
, remember it a raster map like any other one:
g.remove rast=MASK
The simplest analysis we can run is d.histogram
. These are the histograms of elevation and aspect for the whole of our study area. Aspect is calculated counterclockwise from east, thus 0 = 360 = E, 90 = N, 180 = W, 270 = S. See http://grass.itc.it/grass62/manuals/html62_user/r.slope.aspect.html for the manual page of r.slope.aspect
.
Applying built.areas
as MASK
results in these histograms:
Aspect values are counted from 0 to 360 in degrees. So it would be better to plot aspect in a polar diagram instead of an histogram.
The d.polar
module does exactly what we need. Its complete documentation is at http://grass.itc.it/grass62/manuals/html62_user/d.polar.html .
It's handy to directly save the diagram to an EPS file for subsequent operations (inclusion in a LaTeX file, conversion to other graphic formats with ImageMagick, …). Then you can use this command to get your diagram
d.polar map=aspect.5m@PERMANENT undef=0 eps=all.eps
These are the results:
This simple exploratory analysis leads us to understand that in the study area there's a strong preference for sites exposed S-SE, built mostly around 700 meters above sea level.