I have a boundary polyline of an island that is broken into multiple short segments. The island is surround by many other islands. What I want to do is delete the mainland island and convert the satellite islands into polygons. I tried dissolve but that merged the entire file into one feature. I then tried the multipart to single part thinking it would separate the smaller islands from the large one but it broke the entire file back up into the short segments again. Effectively I want to merge/dissolve touching lines so that each individual island is its own, one line feature.

  • Have you tried 'Polygonize' geoprocessing tool? – Jochen Schwarze Jan 26 '19 at 13:39
  • This sounds like a case of Topology Checker doing the job you need, which is to identify gaps and small defects in your data. – Gabriel C. Feb 25 '19 at 14:07

Depends on how your segments are "touching" each other, but one possiblity is Join multiple lines plugin.

It is a nice tool, but please use it attentively, because the input geometries are important.

(1) Input

enter image description here

(2) Output

enter image description here

If the islands are like the No.3 above (segments are met at the end vertices) ,the tool successfully returns closed polygons. If not, the output will be usual "garbage in, garbage out".

  • I have thought about that tool but the layer is extremely complex. I suspect there are a couple of gaps and that is causing the polygonise tool to fail but I have no idea where they are and can't find them manually. – Ski nail Jan 27 '19 at 2:15
  • @Skinail If you want to discuss about Polygonize please address it to Jochen. (Start ID with @ mark will send your comment to Inbox). – Kazuhito Jan 27 '19 at 12:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.