I am trying to find a tool that is similar to "Adaptive Smoothing" (found on ArcGIS) on QGIS. What I am trying to do is eliminate narrow drainages (narrow corridors less than 6 m wide). This is part of my predictive wetland model.

I have tried getting the negative buffer of the polygons (i.e. 6 m) and then I got the positive buffer (6 m). I found that this eliminated the narrow drainages but when I created the polygons, the buffered result didn't maintain the shape of the original polygon.

Is there a way to maintain the shape of a buffered polygon?

This is the before result (note narrow fingers):

enter image description here

Here is the result of de-buffering and buffering. This is almost what I want but I want the buffered result to maintain the shape of the original polygons (minus the narrow fingers):

enter image description here

Is there a way to achieve what I have done but somehow maintain the polygon boundary which was found in the original polygons?

  • For those without access to ArcGIS: can you explain what Adaptive Smoothing does? Can you show us on your picture what you want to eliminate - maybe a preview how the result should look like?
    – Babel
    Commented Nov 21, 2021 at 15:04
  • 1
    Thanks. I updated my comments. Since the original comment, I found some ways to get one step closer to the product I want. The main thing I am trying to determine now is how to maintain the polygon shape of the buffered item.
    – Erioderma
    Commented Nov 21, 2021 at 15:29
  • 3
    Does the intersection of the buffered polygons with the original polygons give you the result you want?
    – Jake
    Commented Nov 21, 2021 at 15:39
  • I would habe had the same idea as @Jake. Erioderma, can you provide sample data for testing?
    – Babel
    Commented Nov 21, 2021 at 15:44
  • I am testing this out as we speak. What would the best way to provide sample data if I don't have success with trying the intersection tool? @Babel
    – Erioderma
    Commented Nov 21, 2021 at 15:58

1 Answer 1


I would do a negative buffer and then a positive buffer something like 1.5 times larger than your negative buffer and then use that to clip your original layer. negative buffer larger positive buffer clipped layer It's not perfect as you lose some of your "fingers" but it works pretty well. To figure out what the ideal buffer sizes are I use a buffer in a geometry generator to play with numbers. geometry generator

  • Great if you could mark it as answered that might be helpful for future users. Also perhaps the title should be changed to 'Remove Narrow Polygon Areas but Retain Shape QGIS' or something.
    – Baswein
    Commented Nov 22, 2021 at 17:57

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