[Qgis-user] Ho to intersect layers with some conditions

[G. Allegri]

I fear it isn't possible to do it in one single step. If I had to do it in
a rush I would:

 - add a column to the grid layer and populate it with the square area.
Your squares are fixed, so you can populate it manually, otherwise the
field calculator could be used to do it
 - do an intersect between you polygon and the grid (Vector ->
Geoprocessing)
 - add another column to the intersection result, and populate it again
with the area, using the Filed Calculator.
 - AT this point you will have the original area and the new area. With
Field Calculator populate a third column with the new area / original area
ratio (x 100 if you want the precentage).
 - Select the squares where the percentega is over 90.

How to obtain the unclipped, original, squares? You can do a spatial join
between the original grid, and the selected squares (above 90) from the
intersection result.

Giovanni

2013/4/11 Levy Vincent <v.levy at cbnbl.org>

>  Hello,****
>
> ** **
>
> I have a layer with a big polygon and another layer which is a grid (made
> of squares 10X10m). The grid is larger than the big polygon and cover it
> entirely. ****
>
> I want to keep only the squares of the grid contained in the polygon. I
> know how to intersect my two layers  to select all the squares of the grid
> inside my “big polygon”.****
>
> The problem is on the border : I would like to select only the squares
> which 90% of their surface is contained in the big polygon.****
>
> Is there any plug-in or another solution to do it easily?****
>
> I hope somebody could help me, thank you for your answer,****
>
> ** **
>
> *Vincent LEVY*****
>
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-- 
Giovanni Allegri
http://about.me/giovanniallegri
blog: http://blog.spaziogis.it
GEO+ geomatica in Italia http://bit.ly/GEOplus
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