[GRASS-user] How can I find average/maximum raster values within a vector area?

George MacKerron george.mackerron06 at ic.ac.uk
Wed Aug 1 16:43:32 EDT 2007

Hi all. I've just started out using GRASS, so I hope this question
isn't too dumb.

I have some raster maps of air pollutant levels in London, by 50m x 50m cell.

Firstly, I have a set of postcode points. I have been able to sample
pollutant levels at these points using v.what.rast. I have also been
able to sample average and maximum levels within small regions
surrounding the points (square regions: not ideal, but there we go)
using r.neighbours (method=average or method=maximum) to produce a new
raster map, followed by v.what.rast.

However, I also have vector data on administrative areas (such as
electoral wards), which are up to a few square miles in area, and I am
trying to discover average and maximum values of the pollutants within
these areas. I have studied the documentation I can locate, but have
not been able to work out how to achieve this.

Any help -- or pointers to where I can find relevant tuturials/docs --
would be very gratefully received.

All the best,

George MacKerron

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