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I have two polygon layers. The first one contains the different “local districts” within a city, and the second one is the “greenery in different land use types”.

An important distinction to make, is that, it is not guaranteed that a particular greenery area, will always fit in a given district (i.e. a greenery area can be shared between 2+ adjacent districts).

When I join the “greenery in land use types” layer to the “districts” one, and I try ask to calculate the sum of my attributes, I get the greenery area sum for each district, I get double counting/summing on the "shared" areas.

Is there any way to consider the whole amount of greenery area that falls in each district, but to ignore the section of greenery that falls in another district?

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  • Read what intersect does, perhaps this is your tool – FelixIP Mar 19 '17 at 18:24
  • Thanks @FelixIP I tried using the Intersect tool, and even though it successfully cropped my polygons, I'm still not getting correct area data, I feel it's still double counting the area. Am I doing something wrong? – nylkoorb Mar 19 '17 at 21:27
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    Feelings are not going to work. Compare totals of intersections area with original area of green. It has to be less or equal original. Summarise per district I'd and transfer results to district table – FelixIP Mar 19 '17 at 21:47
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If you have run an intersect on greenery and districts and are still getting double counts, you may have overlapping greenery polygons.

To correct this, first dissolve the greenery polygons. In the dissolve tool, untick 'Create multipart features'. This will merge all greenery polygons that overlap or touch.

The next step is to run the intersect tool on the dissolved greenery layer and the districts layer.

Finally, calculate the areas of the intersect result. The table of the intersect result will have all the fields from the districts layer, so you can see which district each area corresponds to.

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