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I am drawing administrative regions that have boundaries follow streets in another layer. As these streets are pretty long with many vertices, I don't want to re-trace them. I am looking for a way to "split" the polygon like "split features" tool (the one with the scissors icon).

Before: one whole polygon with a line running through it

enter image description here

After: the line works as a pair of scissors and split the polygon into 2 parts (in the picture below, the polygons were moved apart for illustrating purpose only)

enter image description here

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5 Answers 5

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First you have to union both shapes

enter image description here

Then activate the Polygonizerplugin to reshape the lines to polygones:

enter image description here

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  • My Ubuntu Qgis complained about missing shapely.ops when I tried to install Polygonizer plugin. Right now I don't know how to fix it. I'll have to resolve this problem before trying your solution. Thanks. Oct 19, 2012 at 2:40
  • It works. What took me so long to accept your answer is that I didn't know how to install shapely.ops. It turns out very easy: go to Ubuntu software center, search for "shapely" and install the only one python-shapely package. After that I was able to install polygonizer plugin and tried out your solution. Thanks a lot! Oct 31, 2012 at 10:28
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    I can't install the Polygonizer plugin. Feb 13, 2013 at 21:24
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I solved this problem with the Processing Toolbox, using the SAGA Polygon-line intersection algorithm.

The process might fail (i.e. no split) if the line end is snapped to a vertex point of the polygon. Extending the line a bit into the neighbouring polygon or outside area sanitizes those pitfalls.

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This similar question is for ArcGIS, but may provide you with some ideas from the discussion that you can implement in QGIS.

I also created an ArcGIS model that you may be able to replicate using similar concepts in QGIS. I tried to describe the concepts that I used here.

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  • Thanks for your answer, but right now ArcGIS or programming skill is out of my ability. Oct 19, 2012 at 2:47
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If I understand your question correct, the the GRASS command v.type.bl can be used to convert polygons to lines. see the following post: How do I split polygons into line segments?

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  • I added pictures to clarify the question - thanks a lot. Oct 18, 2012 at 9:25
  • @Cao Minh Tu: thanks, the pictures make it clear, I did misunderstand you
    – Kurt
    Oct 19, 2012 at 5:35
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If you don't have the ArcInfo license, you can use the command "geom.splitpolysbylines" in the Geospatial Modelling Environment. It work perfectly. Make sure, however, that you have ArcGIS 10.1 or ArcGIS 10.0 SP4 and installed "R" 2.12 or higher.

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  • My question was for Qgis (showed in the tag) - I updated the header to make it more visible. Thanks anyway! Nov 16, 2013 at 2:27
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    Sorry about that. Anyhow, if "someone else" has the same type of question, he/she use the option that I suggested above.
    – Doum
    Nov 18, 2013 at 21:05

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