I'm trying to scan plain pdf maps containing color-coded geographic regions and convert them into undifferentiated (I don't actually need them to contain any attribute data) overlays. My workflow is to take one of my color-coded maps, select a few of the color-coded regions via Gimp's "Select by Color" tool, cut those out into a separate layer, then export just that layer with a transparent background as a tiff. I then georeference that tiff, and proceed to polygonize it. Polygonization of poor quality images is causing what should be 100-1000 polygons (map regions) into 1 million polygons, most of which are 1-4 pixels in size (area).
So far a solution hasn't been forthcoming. So on the GIS front, I'm hoping I can at least merge directly adjacent polygons. Here's what they look like:
In QGis, I've tried the "dissolve" tool, the "buffer tool" & the "Multipart(s) to singlepart(s)" tools, as well as the "Densify" tool & and "Simplify" tool.
None have really worked so far. The buffer tool, which has worked in the past, turns the entire area into a single polygon, even when I try to get it to approximate the maximum (99) number of segments. Other methods either do nothing, fill the entire screen with a single polygon, or take literally days to process.
So maybe there is a "Polygonize" method (from raster) that will best do the job here, or maybe its a post-polygonize job. Thanks for taking a look