Thank you very much Micha.<div><br></div><div>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?</div><div><br></div><div>Best,</div>
<div><br></div><div>Manuel</div><div><br><br><div class="gmail_quote">2012/7/16 Micha Silver <span dir="ltr"><<a href="mailto:micha@arava.co.il" target="_blank">micha@arava.co.il</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im">On 16/07/2012 20:22, Manuel Spínola wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Dear list members,<br>
<br>
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?<br>
<br>
</blockquote>
<br></div>
Not exactly "one step" but...<br>
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:<br>
Suppose "buffers" has a label column, and there are landuse categories lu1, lu2, lu3, .... then:<br>
<br>
SELECT b.label AS Buffer,<br>
ST_Area(ST_Intersection(b.<u></u>Geometry, l.Geometry)) AS LandUse1<br>
FROM buffers AS b, landuse AS l<br>
WHERE l.category='lu1' AND<br>
ST_Intersects(b.Geometry, l.Geometry)<br>
GROUP BY b.buff_id;<br>
<br>
If you add columns to the buffers table to hold total area for each landuse category::<br>
ALTER TABLE buffers ADD COLUMN lu1_area float;<br>
ALTER TABLE buffers ADD COLUMN lu2_area float;<br>
....<br>
<br>
then you'd update each column like so:<br>
UPDATE buffers SET lu1_area=(<br>
SELECT ST_Area(ST_Intersection(b.<u></u>Geometry, l.Geometry)) AS LandUse1<br>
FROM buffers AS b, landuse AS l<br>
WHERE l.category='lu1' AND<br>
ST_Intersects(b.Geometry, l.Geometry) AND<br>
b.label=buffers.label<br>
);<br>
<br>
HTH,<br>
Micha<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Best,<br>
<br>
Manuel<br>
<br>
-- <br>
*Manuel Spínola, Ph.D.*<div class="im"><br>
Instituto Internacional en Conservación y Manejo de Vida Silvestre<br>
Universidad Nacional<br>
Apartado 1350-3000<br>
Heredia<br>
COSTA RICA<br>
</div><a href="mailto:mspinola@una.ac.cr" target="_blank">mspinola@una.ac.cr</a> <mailto:<a href="mailto:mspinola@una.ac.cr" target="_blank">mspinola@una.ac.cr</a>><br>
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</blockquote>
<br>
</blockquote></div><br><br clear="all"><div><br></div>-- <br><b>Manuel Spínola, Ph.D.</b>
<br>
Instituto Internacional en Conservación y Manejo de Vida Silvestre
<br>
Universidad Nacional
<br>
Apartado 1350-3000
<br>
Heredia
<br>
COSTA RICA
<br>
<a href="mailto:mspinola@una.ac.cr" target="_blank">mspinola@una.ac.cr</a>
<br>
<a href="mailto:mspinola10@gmail.com" target="_blank">mspinola10@gmail.com</a>
<br>
Teléfono: (506) 2277-3598
<br>
Fax: (506) 2237-7036
<br>
Personal website: <a href="https://sites.google.com/site/lobitoderio/" target="_blank">Lobito de río</a>
<br>
Institutional website: <a href="http://www.icomvis.una.ac.cr/" target="_blank">ICOMVIS</a><br>
</div>