I'm still quite new to QGIS and I'm using it to display and analyze my soil data. I have point information on the distribution of the soils in a specific area and I need to create a soil map from that. I'm using QGIS 2.2.0 Valmiera and I used the voronoi polygons function to interpolate the areas between the points. Now these are very edgy but in soil science it is custom to have smooth bent lines in the soil maps because that rather represents the nature of soil distribution then straight lines.

Is there another function or algorithm that interpolates smooth polygons, or is there a way to smooth the voronoi polygons? I have seen that there a some threats on smoothing polygons already but none refer to exactly this problem.

Below is a picture of the polygons I've got so far.

Below is a picture of the polygons I've got so far:

  • Can you draw by hand a sketch about the desired result?
    – user30184
    Jun 13, 2014 at 11:24
  • 1
    Smoothing those lines would introduce significant error, since it's unsupported by the data. Worse yet, it would look like a more accurate dataset and therefore conceal the randomness.
    – Vince
    Jun 13, 2014 at 11:30
  • Is your soil data in classes (nominal scale) or continuous numerical values (ration scale)?
    – underdark
    Jun 13, 2014 at 15:57

1 Answer 1


As stated, it is an operation that is unsupported by the data to make smooth polygons out of these data.

Ask yourself this question: how would you decide whether the representation that you would make would be more accurate than the Voronio diagram that you have created?

For the danish soil map for instance, the sample density is much much higher and supported by other data - therefor the results can be the detailed map that you require.

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