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

[David Finlayson]

Forgot to CC grass list

On 8/1/07, David Finlayson <dfinlayson at usgs.gov> wrote:
> I think you want the command r.statistics. You will need to convert
> your administrative areas vector map into a raster map where each area
> has a unique ID. Then run r.statistics on the pollution map using the
> administrative areas raster as the cover. This tool builds a database
> table with the min,max avg, etc statistics of pollution for each area
> id.
>
>
> On 8/1/07, George MacKerron <george.mackerron06 at ic.ac.uk> wrote:
> > 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
> >
> > --
> > George MacKerron
> >
> > _______________________________________________
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> > grassuser at grass.itc.it
> > http://grass.itc.it/mailman/listinfo/grassuser
> >
>
>
> --
> David Finlayson, Ph.D.
> Operational Geologist
>
> U.S. Geological Survey
> Pacific Science Center
> 400 Natural Bridges Drive
> Santa Cruz, CA  95060, USA
>
> Tel: 831-427-4757, Fax: 831-427-4748, E-mail: dfinlayson at usgs.gov
>


-- 
David Finlayson, Ph.D.
Operational Geologist

U.S. Geological Survey
Pacific Science Center
400 Natural Bridges Drive
Santa Cruz, CA  95060, USA

Tel: 831-427-4757, Fax: 831-427-4748, E-mail: dfinlayson at usgs.gov