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I have a layer with a lot of polygons. Now I want to filter all polygons that are very narrow. For example, the polygons show living space. But I'm only interested in large living spaces. Function $area does not help here, as there are also very long and narrow surfaces. Does anyone know a function in QGIS that comes to this output via filtering x and y?

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  • You could use the point of inaccessibility and its distance to the polygons border?
    – Erik
    Commented Jul 5, 2019 at 11:50
  • Do you mean checking the difference of max_x minus min_x (or y) is very small? So you can do QGIS expression to select them according to a defined threshold.
    – etrimaille
    Commented Jul 5, 2019 at 11:51
  • I tried that: new field -> xmax ($geometry) - xmin ($geometry). And the same for y. But I'm still missing something. That does not help me yet.
    – hugo
    Commented Jul 5, 2019 at 12:02
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    @hugo - If you want to ignore long, narrow polygons which, for example, have an average width of 10m, you could use a query like area(buffer($geometry, -5)) > 0. This query creates a negative buffer (i.e. inwards) and if the area of the buffer is greater than 0 then that polygon has a greater width.
    – Joseph
    Commented Jul 5, 2019 at 12:09
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    This works very well! Thanks! Can you explain to me what significance the -5 has here?
    – hugo
    Commented Jul 5, 2019 at 12:20

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If you want to ignore long, narrow polygons which, for example, have an average width of 10m, you could use a query like:

area( buffer($geometry, -5 )) > 0

This query creates a negative buffer (i.e. inwards) and if the area of the buffer is greater than 0 then that polygon has a greater width. You can change the value to set a threshold more suited for your needs.

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