I'm currently doing a research project analyzing how cities evolve over time and were wondering if there were any good online databases for finding historical building footprints. I've been looking around for a while now but couldn't find what I was looking for. Any help would be greatly appreciated.
Very good question. Unfortunately OpenStreetMap will be of no use here. Maybe there is are established ML techniques to extract buildings from georeferenced historical maps, like the Dufour map in Switzerland and others.
E.g. something like this: http://lazarus.elte.hu/avhm/proc/AVHM_proceedings_01_Drolias.pdf