Here are my polygons of town blocks.

enter image description here

The colored towns are considered as areas where they have the same post code.

What I eventually want is to make seamless polygons where there are no gaps between polygons (please see the screenshot below)

enter image description here

What functions should I use to complete my mission?

3 Answers 3


Since there is the "post-code" field, it is suggested to use the "Convex Hull" tool from the Processing Toolbox (Ctrl+Alt+T), can be found in Vector > Geoprocessing Tools > Convex Hull.

Hint: Create Convex Hulls based on a field.

  • 1
    right. Convex Hull! I couldn't think of it but thanks a lot!
    – Pil Kwon
    Aug 27, 2018 at 5:19

Wouldn't you want a concave hull? A convex hull will give you a large amount of area that isn't part of the block. For example, a convex hull would fill in that big gap in the "hook" park of block 1.


You can do a morphological closing (buffering outwards and then inwards by the same amount) to close the gaps. It will cause slight distortions to inner corners, though, so your final areas will be changed.

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