[GIS] How to digitize polygons from georeferenced raster file

Question

I used QGIS to georeference a raster file of a custom US map. The map has features which are not strictly defined by state borders. I would like to digitize the map by creating contiguous borders for each feature. I tried that a few different way, but none of them really worked:

• traced the borders with polylines, and digitizing with the Polygonizer plugin. The plugin kept crashing.
• used Conversion > Raster > Vectorize (Raster to Vector). That one worked, but the result was many overlapping polygons for each feature, each with slightly different borders.

I have somewhere between 50-100 different raster images to process, which is why any automated solution is highly preferred. I'm new to GIS software, but could easily pre-process the images if needed, either manually or with a custom script (using Python/PIL, ImageMagick, Photoshop batch processing or similar tools).

Thanks for any pointers!

Original

Georeferenced image

Answer 1

What you could do is:

1. In the original image, fill each area with a unique color, e.g. with Gimp
2. Georeference
3. Run Raster to Vector
4. Clean up the polygon geometries manually