I have different polygons in layer a_input. The Polygons are adjacent and connected inside the layers and it should be. The Polygons in layer a_input have to fit adjacent to a polygon of layer 2 b_input. I tried v.edit and v.overlay but didn't find the right options to get the result I wanted.

In the Picture, the green Polygon is the b_input and the black lines are the boundaries of the polygons in a_input. They have to fit the boundaries of the polygon in b_input. The red line is the result of v.edit.


How to solve such question in QGIS?

  • Please open an enhancement ticket for that at trac.osgeo.org/grass
    – markusN
    May 9, 2018 at 19:44
  • How many of these do you need to do/how large an extent will you be working on? You can manually fix this in several ways, such as selecting the two target polygons and tracing the black lines with the reshape tool. In semi "batch" mode you could run a union to split your a with the b polygons and then manually go around to select and merge the newly split polys with their appropriate target poly. You could also use selection queries based on the combined attributes to select and merge.
    – John
    May 15, 2018 at 13:05
  • In the moment there are only around 300 polgons and they have to be adjacent together only fit to the surrounding polygon. The tool have to be automatic.
    – Torsten
    May 15, 2018 at 15:39

1 Answer 1


I think this type of vector edit is much straightforward if you want to do it in QGIS.

Bring both the vectors in QGIS and turn-on the edit mode for the vector you want to modify. Then you can edit the nodes you want with the 'Node Tool'

It is not exactly clear to me what you exactly mean by "adjacent and connected inside", but if you need the 2nd vector layer almost similar to the 1st layer, it would be easier to make a copy of the 1st layer and then adjust it rather than try to edit a new layer. In the latter case, this post can help.

If I'm misinterpreting your question, please explain a bit more.

Adding this after reading your comments.....

Have you tried the v.clean in GRASS? Its a fantastic tool for this kind of cleanup job. There are quite a few options with what you can use as a 'Cleaning tool' and how you set the threshold. I would first try the 'Snap lines/boundaries' tool with different thresholds. Please see the screenshot of this tool below.

v.clean tool options in GRASS 7.4

  • Thanks for the answer. So far I can see works v.clean only in one layer. I have to fit the polygon of layer a into a surrounding polygon of layer b by keeping the internal relations of the polygons in layer a as there were befor (adjacent). v.edit uses a background layer but is not clear for me what it does with that background, it doesn't work as I want. So I use a tool that automatically expand or shrink the edges of some polygons from layer a to layer b. In ArcGIS there is a snap tool that does that work more ore less but I need OpenSource solutions.
    – Torsten
    May 16, 2018 at 11:38

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