[GRASS-user] Aggregate a classification map according to a vector file

Pedro Roma pedroroma1982 at gmail.com
Mon Jan 18 08:17:59 EST 2010

Thank you all. I thing I have managed to do this using r.statistics firstly
converting county polygons to Raster.
THank you guys

By the way, is there any special requirement, besides being a CELL, for base


On Mon, Jan 18, 2010 at 12:52 PM, Markus Metz <
markus.metz.giswork at googlemail.com> wrote:

> Pedro Roma wrote:
>> Greetings all
>> As far as I can see, r.statistics (
>> http://grass.itc.it/grass64/manuals/html64_user/r.statistics.html) uses
>> as cover and as basis a RASTER map. But, "All cells in the base layer are
>> considered one object for the analysis". This is not what I want because I
>> want base layer to be a polygon not a cell. Or Am I reading this wrong?
> You're right, but you can easily convert vector to raster. In this case,
> first set the region to match your cover map, then something like
> v.to.rast type=area
> then r.statistics
> v.what.rast also converts the vector to a raster first, then runs
> statistics. v.what.rast would be the best solution unless you want the most
> frequent category.
> Markus M
>> On Sat, Jan 16, 2010 at 9:59 AM, Markus Metz <
>> markus.metz.giswork at googlemail.com <mailto:
>> markus.metz.giswork at googlemail.com>> wrote:
>>    Markus Neteler wrote:
>>        Pedro Roma wrote:
>>            Greetings all
>>            A few emails that people sent, regarding classigication
>>            operations GRASS
>>            were extremely helpful :)
>>            But now, I have one question:
>>            I need to do some aggregation of the classification map
>>            according to regions
>>            specified in a vector file. What I mean is, for each
>>            county I need to have
>>            an aggregation of all classified pixels in order to have
>>            only one value that
>>            represents that county.
>>            E.g. I have a land cover classification for my region and
>>            now I need to
>>            aggregate the classified map according to my counties in
>>            order to have a
>>            vector map in which each county is represented by its more
>>            frequent
>>            classification.
>>            Is this possible in GRASS? Was I clear :D ?
>>        Could this be of interest?
>>        Addons: r.univar.zonal
>> http://svn.osgeo.org/grass/grass-addons/raster/r.univar2.zonal/r.univar.zonal.html
>>    Or r.statistics with method=mode, gives you the most frequent
>>    value in cover map for each value in base map. AFAIK,
>>    r.univar[.zonal] doesn't have modal as output.
>>    Markus M
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