I have a shapefile which contains a lot of polygons which define airspace. These polygons overlap and this is fine (e.g. different airspace configurations for the same airport).

My problem is that many of the polygons could share common vertex but instead they each have a minutely different list of points. This can be seen in the image below: the inner circle is defined twice with points that are almost in exactly the same place but not quite.

So close but so far

What I am trying to do is replace points that are currently extremely close with a single point and use this for all polygons in the layer. It's not realistic to do this manually. I've tried using QGIS dissolve and also eliminate sliver polygons but these seem to be intended for polygons that are not supposed to overlap. It's going to be difficult to convert to lines and back again without losing details associated with overlapping polygons.

  • 1
    The question is a more complicated version of this one: gis.stackexchange.com/questions/143695/…. Once you have made boundaries to snap it is possible to simplify the layer without creating slivers and gaps between the polygons. At least OpenJUMP has a topology aware tool for that.
    – user30184
    Apr 23 '15 at 21:57

I'm not sure that this will work but you could try smoothing/simplifying the shapefile. This can be done in QGIS (alternatively try http://mapshaper.org/). I would try it myself but I don't have any shapefile data similar to what you've described.

  • Thanks for your input. I have tried this, but it seems to simplify each polygon individually so no common points generated and shared between nearby polygons.
    – Dan
    Apr 23 '15 at 21:04
  • 1
    Ah- thought it was too simple to work. Good luck, hope it works out.
    – Eamon
    Apr 23 '15 at 23:00

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