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I would like to split a shapefile in qgis according to how the polygons overlaps. Don't know how to though? See pic for explanation:

enter image description here

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So..did it work? –  Shepherdjo Aug 2 '12 at 6:19
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3 Answers

I think I found a method. It s a grass function included inside the sextante plugin. See the screenshot. I did a test with a shapefile that looked like yours.pic

More Details:

  1. It is best to install QGIS Sextante Plugin. So you do not have to worry about importing/exporting to grass datasets.
  2. The tool is Located in Sextante toolbox > Grass Commands > Vector > v.overlay

  3. Just open the tool and use the default parameters and you get the results in a new layer

enter image description here

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I am more familiar with ArcGIS than QGIS but I just did a brief search and think this would work:

1) Use the Union tool (as suggested by Darren Cope) to create your 7 features.
2) Under Data Management Tools use "Join attributes by location" and take the sum of the number of your original (purple in your map) polygons that overlap your new 7 features.

Thus where there is only 1 original poly, the new field = 1, where there are 2 polys, field = 2 and so on.

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Here is a good site with info on the QGIS equivalent of a Spatial Join: maps.cga.harvard.edu/qgis/wkshop/join_spatial.php –  AlmaThom Aug 1 '12 at 22:25
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The standard QGIS Georeferencing tool "Union" will give the same result.

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i can't get it working as per the asker's requirement..i gave input and union layers the same..are you sure it would work? –  vinayan Aug 1 '12 at 16:23
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