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I have a shapefile with polygons (municipal.shp) which contains a variable (float numbers) for each municipality of an area. I want to distribute these values into a vector grid (grid.shp) with different projection. So, the splitting should be based on the area proportion of the value. In the image below you can see how the files look like and how the output should be.

enter image description here How I could do that in QGIS?

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  • I don't get the point about the "area proportion", or more precisely, I don't get how proportions are connected to tilting the grid. Could you explain it in detail, please? – Erik Feb 4 '19 at 16:03
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If I understand your question correctly you can do the following:

First, both of your layers, the municipalities and the grid, need to be in the same metric projection.

Now you can calculate the value per m² of municipalities using field calculator and store it in a new field, lets say valuem2. Use "value" / $area.

enter image description here

Now perform an intersection of municipalities and grid.

enter image description here

It will look like this (id_2 is the grids id):

enter image description here

When you now calculate the new value using "valuem2" * $area you will get the new proportional value into each new splitted polygon.

enter image description here

Now you can reproject your final layer into whatever you want to have it.

Your final product will look like this. Value per m² is represented in a blue color ramp. Value New is represented in the size of circles at the centroids. Additionally labels with all three values. The only one of interest for you in this final result is valuenew. You can delete the other columns to avoid confusion.

enter image description here

  • value is the original absolute value of your municipalities.
  • valuem2 is the relative value of value of your municipalities.
  • valuenew is the absolute value of your new polygons, the intersection of municipalities and grid. This will be your final product. It was calculated by the new polygons area multiplied with valuem2.
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  • I tried what you suggested but I have the following problem: If a polygon (municipality) has the value of 100 and overlaps 2 grid cells of the final grid then in the final intersection.shp both grid cells have taken the value of 100. The correct would be that the value of 100 would be distributed based on the area of the polygon covered in the grid cells. – Nat Feb 4 '19 at 19:53
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    @Nat Yes thats true, you can delete the value field in the intersection layer to avoid confusion. You will recalculate the value via valuem2 * $area as shown in the last step: The value of interest in your final layer will be valuenew. Will add a screenshot to my answer. – MrXsquared Feb 4 '19 at 19:58
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    @Nat added screenshot and short explanation. Hope it helps understanding it. If not let me know. – MrXsquared Feb 4 '19 at 20:24

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