I'm looking for historical shapefiles of city boundaries in the United States, for the time period 1920 - 1950. I know these won't be available for every city, especially small ones, but I'd like as many as I can.
Other questions, like this one deal with MSAs and CBSAs, which I don't think existed at the time. If all else fails, I can use those.
Other resources like the National Historical Geographic Information System (NHGIS), Duke, and the Newberry Library don't seem to have these either.