I have a scanned map that has areas of different colours. I want to create polygons for each area and would like to avoid doing it manually (tracing over the shapes).

Is there a way to do this? I do not have ArcGIS - am using QGIS.

I have tried various feature extraction options to no success (probably choosing the wrong options).

I have tried creating a layer of just the e.g. blue sections with everything else transparent, importing that, and then polygonising this - but I just get a polygon the size of the whole area.

I have also tried to follow How to digitize a raster automatically (Processing toolbox no longer exists, options I tried in Orfeo unsuccessful); and https://docs.qgis.org/2.2/en/docs/training_manual/forestry/stands_digitazing.html (polygons whole area).

I have something like this example map

except the colours aren't quite so clear - it's a shaded map overlaying satellite imagery, so there's lots of tiny "gaps", but I can fill these without too much hassle if needed.

  • 3
    If it's scanned you'll probably need to do a supervised classification gis.stackexchange.com/questions/228684/… Aug 4, 2017 at 4:54
  • have you tried ArcScan?
    – Nxaunxau
    Aug 4, 2017 at 5:51
  • MichaelStimson - I'll give that a try. nxaunxau - I don't have ArcGIS unfortunately, working with open source QGIS. I'll update the question to make that clear.
    – Esme_
    Aug 4, 2017 at 6:59


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