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I am trying to use the "Split selected features with selected line from another layer" tool from the plugin Digitizing Tools in QGIS. Sometimes, this tool works with my shapefiles but sometimes it won't for reasons I can't figure out. So far, my troubleshooting skills have led me to check:

a) the projection for the project, the polygon and the polyline is all the same

b) the polyline extends beyond the polygon I want to cut

c) if I create a new polyline in my polyline .shp file, I can use it to cut the polygon (but I need to use the pre-existing polylines for cutting) [I tried this after reading the bug report http://hub.qgis.org/issues/15312 ]

I had wanted to add this question as a comment to a previous Question on this tool but my StackExchange standing isn't high enough: Is there a way to split polygons by several lines in QGIS?

  • Couldn't reproduce your problem on my machine. Please provide some data. – dof1985 Jul 26 '16 at 15:38
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    After trying to convert my polyline into a polygon, I discovered the problem in my polyline file when it was all wonky. The polylines that wouldn't work were lines that I had initially drawn as separate lines and then joined using the basic tool. What I hadn't realized was that my polylines didn't quite join up (there were very small gaps between my polylines, too small to see until I zoomed in really close). I had a multipart polyline instead of a simple single polyline. Once I had edited the lines to join properly, the split selected features tool worked. – user3386170 Aug 2 '16 at 19:13
  • Good job. I guess running topology on a vector file could have been helpful. Can you add it as an answer, maybe with a print screen that give an example of the solution? It will make your question much more valuable for the community. – dof1985 Aug 2 '16 at 19:34
  • I tried to recreate the problem in order to show print screens of the problem and its solution. However, this time, multipart polylines (with gaps between segments) are working to split a polygon. So... that wasn't really my problem. Also, there were no errors in the geometry. I can say that setting the snapping (accrochage in fr) distance to something reasonable (30 pixels instead of 2px) helped to unite the polylines in order to get one single polyline. – user3386170 Aug 9 '16 at 17:28

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