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I want to extract contour lines from a scanned map. I success to georeferance and I make line shapefile and try to extract contour line manually. But there are too many lines in the map.

I install OBT toolbax in qgis. but my image is just image. No data in there. How can I extract contour? Are there some method to trace some line which have specific color?

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After georeference, try to make your image vector using Conversion tools but it is hard to make the data as you wish with this method, find DEM and extract the contour line from DEM of your area to the scale of your map enter image description here

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  • Thank you for your advice! but my map is made at 1956, So I cannot use dem data. I try convert to vector!! Dec 2 '17 at 10:44

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