I have numerous marine shapefiles that need to be simplified for display purposes.

I need to eliminate the coastlines of land entirely and be left with just polylines in the ocean, as the Large Marine Ecosystems dataset already does: LMEs with coastlines LMEs without coastline

I'm using QGIS for this.

  • There is the QGIS tag here, but I can't see what you have tried to do with it (you only mentioned mapshaper, which is an external service for simplification). – mgri May 17 '17 at 7:36
  • Can you clarify what you mean by "I need to eliminate the coastlines of land entirely and be left with polylines". If the 'ppolylines are not coastlines, what are they and how are they currently represented in your data? – MappaGnosis May 17 '17 at 10:53
  • @mgri I'm looking for solutions that can be implemented within QGIS because the external program mapshaper was not helpful for me. – srha May 17 '17 at 17:12
  • @MappaGnosis I actually just deleted that part of the question as you're right, it was just too confusing! I'm going to be posting that as a seperate question, hopefully better worded. However, is the first part clear? – srha May 17 '17 at 18:00
  • Does the data of the shapefiles not contain a column for the coastlines? If so, then with a simple query you could remove the coastlines to be left with the "oceanlines". – Konan Pruiksma May 18 '17 at 8:59

You can use the Difference tool in QGIS to erase a land polygon from the polylines.

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