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I have a large number of polygons that are overlapping. I'd like to create a heat map and plan on using raster calculation to do this. My plan: to give each polygon a raster value of 1, and adding them up. But, when I convert to raster, it will only the entire shape so that all overlapping polygons have the raster value of 1.

Can I make it convert the individual polygons? I'm doing this in QGIS but come from an ArcGIS background, so either explanation may give me enough to get this done.

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    There is a great blog post on this subject by ESRI called "More adventures in overlay: counting overlapping polygons with spaghetti and meatballs". It may give you some ideas: blogs.esri.com/esri/arcgis/2012/11/13/spaghetti_and_meatballs – Aaron♦ Feb 18 '14 at 20:09
  • Not really great at the old indept questions but first thing that strikes me is why not do a spatial query first for the partsof a polygon which overlap? – Ger Feb 19 '14 at 9:25
  • The Parts that overlap, may actually have more than just 2 overlaps, maybe even 10 overlaps. I'm working on the spaghetti and meatballs method. Spatial join is taking a while since I had so many chopped up pieces – jpmaniac87 Feb 19 '14 at 17:03
  • Aaron, that article actually ended up being exactly what I needed. I had some issues with summing the spatial join, so had to go a slightly different way, but I got what I needed. Thanks! – jpmaniac87 Feb 19 '14 at 18:45
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This seems to be the ArcGIS solution. Hopefully this can guide you in QGIS.

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

  • This is excellent! Thank you. The only thing... I don't believe QGIS can do the dissolve based on the count, which is a shame. Do you know any other options or does anyone know if QGIS can, in fact, handle this? – jpmaniac87 Feb 19 '14 at 16:52

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