I'm working on a dataset of house searches - 1 polygon for each area in which people want to find a house from an online search tool.

This produces many overlapping polygons. It would be great to get a basic understanding of the places that are most frequently searched.

You can do this in QGIS and other programs using transparency:

enter image description here

But ideally, you would create a new layer with the search density for each cell in a grid. This is exactly what the "feature density" algorithm does in ArcView 3.2 and I've seen it work to great effect. It creates a raster map from a mass of overlaid polygons.

So the question is: is there an implementation of this algorithm for my polygon dataset for open source programs. I'm an R and QGIS user so one of those would be preferable. Many thanks!

  • mhh, Can't you just specify an individual integer value for each feature type and then rasterize your vector layer using your newly field? This should return you a raster, where the cells value is the sum of your fields integers and therefore kinda represents density of sth.
    – Curlew
    Jun 15, 2013 at 6:53
  • Hi Curlew, that sounds like a sensible solution to me: simple work around. Could you be more specific about which rasterize function (and in which program) you are referring to though. Would it create a new raster layer for each polygon and then add the cell values, or add them all up automatically?. Jun 15, 2013 at 13:25

1 Answer 1


In GRASS GIS you can achieve the functionality as follows:

All this can be easily put into a single script. Using the standard GRASS GIS Script parser lines as well, it would auto-generate the GUI, too.

  • Thanks for the suggestion - I've tried to test this but for some reason GRASS doesn't like my data (it loaded other shape files fine). I'll try it again once I've altered the attributes that I think are causing the problem... In the meantime: any ideas how you specify the cell size of the raster output of this approach? That's one of the big advantages of the ArcView 3.2 algorithm. Jun 15, 2013 at 13:28
  • What error do you get with that file(s)? For the cell size: obviously you can specify it also in GRASS GIS, see here: grasswiki.osgeo.org/wiki/Computational_region
    – markusN
    Jun 16, 2013 at 6:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.