For a task I have several maps created with GIS that look like the following:

Map view

I am mainly interested in the colored zones that aren't roads (red) or rivers (blue) and would like to turn these into vectors for further spatial analysis. The extraction of this by a simple Raster to Vectors gives me incomplete lines/polygons because the edges of these zones aren't sufficiently sharp.

I have tried some approaches using reclassify values (with SAGA) to clean up the edges somewhat, edge detection using the Orfeo Toolbox, and raster calculator to make the non-white values stronger, but this doesn't seem to lead to sharper edges. Because these zones have a lot of edges, manual digitizing of the edges would be too time-consuming.

Are there any ways to automatize this process?

1 Answer 1


Not automatization (strictly speaking), but one good helper tool would be Gimp Selection Feature plugin.

It enables us to access Fuzzy selection tool of Gimp 2.10, and returns a polygon layer taken from the area you have chosen.

enter image description here

When I tested it on your posted image, Threshold value set at 60.0 was good at differentiating the blue river and surrounding green area (it depends on your CRS, of course).

  • This seems to work for this problem, although I've had to adjust the threshold value a bit down (to 20) to get the lighter colored pink zones separated from the white background. Thanks!
    – Weece
    Nov 7, 2019 at 16:42

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