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I have some polygons that share common boundary. I want to create some small space buffer between it, so no polygon has shared the same boundary. Is there any way to do it instead of manual adjust the polygon? The picture describe what I want. I'm using QGIS or FME to do it.enter image description here

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    You could buffer the polygons by a very small negative amount which will result in a small gap between adjacent polygons and only a minor difference where there is no adjacent polygon - simplest case where the other boundaries don't need to be in the same place. – Michael Stimson Feb 10 at 4:43
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    Just to confirm, the dimensions show 100m as the full extent for both. Where does the extra space come from? Do the rectangles stay the same size and just equally shift away from each other? Or are the rectangles losing width? And they are all the same shape correct? – Rex Feb 10 at 5:04
  • @Rex the rectangles will losing the width. So, the changes would be on part of boundary that touch each other only (not all). And the polygons come in different size and shape. – prawirs Feb 10 at 5:53
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Starting with a polygon layer A:

enter image description here

Dissolve polygon layer A -> Polygon layer B

enter image description here

Buffer B by a tiny negative amount -> Polygon layer C

Zoomed right in you can see the difference:

enter image description here

Convert polygon layer A to Lines -> Line layer D

This looks the same as the original polygons but its represented by lines which means we can cut lines out of it:

enter image description here

Intersect Line layer D with Polygon layer C -> Line layer E

enter image description here

Layer E is now just the shared borders of your original polygons minus the "tiny negative amount" at each external edge. That "tiny amount" should be much smaller than your desired separation distance, and really only has to be enough to be mathematically inside your external border.

Buffer Line layer E by your desired separation distance -> Polygon layer F

enter image description here

Difference original polygon layer A with polygon layer F -> Polygon layer G

enter image description here

Layer G is the final result.

This could be made into a Graphical Model in the QGIS Toolbox.

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  • oh wow..thank you for share the solution. it's really make sense. – prawirs Feb 10 at 13:10

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