Thank you very much Micha. Your suggestion is based on writing a code, right? I am doing this for teaching purposes, is it possible to do the same based on the menu of QGIS?
Best, Manuel 2012/7/16 Micha Silver <[email protected]> > On 16/07/2012 20:22, Manuel Spínola wrote: > >> Dear list members, >> >> I have a landuse layer and another layer with 20 circular polygons >> (buffers) and I want to obtain the amount of each landuse category within >> each circular polygon. I tried "clip" from Geoprocessing Tools but I dont >> get the information individualized for each circular polygon. Is it >> possible to get the landuse within each circular polygon in one step? >> >> > Not exactly "one step" but... > If you don't mind to drop the vectors into spatialite, then a query can > update the buffers layer with area of each landuse category as follows: > Suppose "buffers" has a label column, and there are landuse categories > lu1, lu2, lu3, .... then: > > SELECT b.label AS Buffer, > ST_Area(ST_Intersection(b.**Geometry, l.Geometry)) AS LandUse1 > FROM buffers AS b, landuse AS l > WHERE l.category='lu1' AND > ST_Intersects(b.Geometry, l.Geometry) > GROUP BY b.buff_id; > > If you add columns to the buffers table to hold total area for each > landuse category:: > ALTER TABLE buffers ADD COLUMN lu1_area float; > ALTER TABLE buffers ADD COLUMN lu2_area float; > .... > > then you'd update each column like so: > UPDATE buffers SET lu1_area=( > SELECT ST_Area(ST_Intersection(b.**Geometry, l.Geometry)) AS LandUse1 > FROM buffers AS b, landuse AS l > WHERE l.category='lu1' AND > ST_Intersects(b.Geometry, l.Geometry) AND > b.label=buffers.label > ); > > HTH, > Micha > > Best, >> >> Manuel >> >> -- >> *Manuel Spínola, Ph.D.* >> >> Instituto Internacional en Conservación y Manejo de Vida Silvestre >> Universidad Nacional >> Apartado 1350-3000 >> Heredia >> COSTA RICA >> [email protected] <mailto:[email protected]> >> [email protected] <mailto:[email protected]> >> >> Teléfono: (506) 2277-3598 >> Fax: (506) 2237-7036 >> Personal website: Lobito de río <https://sites.google.com/** >> site/lobitoderio/ <https://sites.google.com/site/lobitoderio/>> >> Institutional website: ICOMVIS <http://www.icomvis.una.ac.cr/**> >> >> This mail was received via Mail-SeCure System. >> >> >> ______________________________**_________________ >> Qgis-user mailing list >> [email protected] >> http://lists.osgeo.org/**mailman/listinfo/qgis-user<http://lists.osgeo.org/mailman/listinfo/qgis-user> >> >> This mail was received via Mail-SeCure System. >> >> >> > -- *Manuel Spínola, Ph.D.* Instituto Internacional en Conservación y Manejo de Vida Silvestre Universidad Nacional Apartado 1350-3000 Heredia COSTA RICA [email protected] [email protected] Teléfono: (506) 2277-3598 Fax: (506) 2237-7036 Personal website: Lobito de río <https://sites.google.com/site/lobitoderio/> Institutional website: ICOMVIS <http://www.icomvis.una.ac.cr/>
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