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Here is my question:

  • I have a polygon shapefile represent the whole country area.
  • A polyline shapefile(with a bunch of line boundaries) represent the province boundaries

So, how to decompose the polygon by the polyline inside and get the shapefile file with each province independently?

I'm a new user of QGIS.

I have done the work of combine inner/outer boundaries using MMQGIS->merge layershows like this:

http://i4.tietuku.com/cfcd52e6886109fa.png

But the next step Change this polylines into polygons I can't cope with

  • The post about cut the shapefile using digitizing tools didn't work for me
  • When I use vector -> Geometry tools -> polyline to polygon, the result shows like this:

http://i4.tietuku.com/7bcda0980879ff24.png

It seems that the inner boundaries had none effect.

  • 2
    Would this post help? Cut polygon shapefile by line shapefile – Joseph Jan 15 '16 at 11:53
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    Most welcome! The tool suggested in the post allows for selected polygons to be split by a single line. If you have multiple lines in your line layer, you could dissolve them into a single line. – Joseph Jan 15 '16 at 11:57
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    If both the polygon and the interior polylines are not coming from the same data source it is very likely to deal with precision issues. Eg polylines actually do not touch or cross the boundary. In this case it might be an option to convert the polygon to polylines, construct a topological correct polyline mesh, and convert to polygons. Dangling lines, undershot are keywords to search for. – Detlev Jan 15 '16 at 16:46
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I think you're asking the same thing here as in your other question How to combine two polyline shapefile together. See my answer to that question.

  • Thanks for your answer. I have combined these two polyline shapefile. But I can't transform it into a bunch of polygons. Wish for your reply. – Han Zhengzu Jan 17 '16 at 14:09
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    I'm not sure why it's not working for you, unless the inner boundary lines are not snapped to the outer boundary. Are you able to upload your two original shapefiles so I can take a look? – SpatialSuccess Jan 17 '16 at 21:49
  • That's very kind. I upload two shapefile in google driverhere, named "Inner line" and "Out line" separately. – Han Zhengzu Jan 18 '16 at 1:50
  • I'm not able to load your outline file, probably because the .shx file is missing. If you can upload again I can check it out later today. – SpatialSuccess Jan 18 '16 at 21:02
  • Forgot to add the link here – Han Zhengzu Jan 21 '16 at 2:48

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