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I have a polygon layer containing habitat types. It looks something like this: enter image description here where dark green is forest, yellow are open lands and the other signatures different other habitat types. In order to get something like a forest edge-line, I'd like to create a line shapefile representing those linear structures where forest and open land touch each other. I could of course use the polygons to lines tool in QGIS and then select the forest edge lines by hand - however, my data are too large for this procedure.

Any suggestions on how to approach this problem in QGIS or R? Please note that - unfortunately - I am not familiar with python at all.

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  • Would it suffice to dissolve the internal boundaries where the code is the same on both sides, leaving you with polygon features? st_union from the sf package? Commented Nov 22, 2017 at 21:38
  • Dissolve as a first step is a very good idea. I tried in QGIS with promising results. I wonder whether there is a QGIS-option to create the forest edge lines. Commented Nov 22, 2017 at 23:49

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In the end, I followed this workflow:

first step:

  • dissolve original polygons using fields
  • polygons to lines on the resulting layer
  • delete all non-forest lines

enter image description here

second step in order to delete the outlines where the original layer extend ends:

  • dissolve original polygons without using fields
  • tiny negative buffer on the resulting layer
  • clip lines layer with buffer layer

The result looks like this:

enter image description here

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  • Nice, you did this in Q? Can you share the data or a similar example, it'd be interesting to get the R code for this. Commented Nov 29, 2017 at 20:28
  • Yes, this was done in QGIS. You could use any set of overlaying polygon layers, I suppose. Commented Dec 1, 2017 at 8:46

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