[Qgis-user] Getting landuse information for several circular polygons

[Manuel Spínola]

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 <micha at arava.co.il>

> 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
>> mspinola at una.ac.cr <mailto:mspinola at una.ac.cr>
>> mspinola10 at gmail.com <mailto:mspinola10 at gmail.com>
>>
>> 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
>> Qgis-user at lists.osgeo.org
>> 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
mspinola at una.ac.cr
mspinola10 at gmail.com
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/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20120716/c220ebad/attachment.html>