Funny how this pops up on hacker news today. I have been working on an off and on again project in the same vein. But instead of sanford maps, I have been ripping and downloading GLO surveys. I now have about 3TB worth of 200k+ mid 1800 surveys done by the USGS (GLO at the time). My next step was to create a method of presenting this data. Do you think that your OHMG would help me here?

Its a similar problem that you faced, stripping off the extra image data from the map, then overlaying them on a base map. I might have a slightly easier time, since these surveys mostly line up to existing township/ranges of the PLSS, not at individual house/street level like the sanborn maps. I've manually done the process many times, most in ArcGIS, but have used a few others (like oldmapsonline). Your site was new to me, and the presentation looks great.

Here's an example of the type of survey I'm working with. https://www.oldmapsonline.org/en/maps/06317a09-5426-41e0-aa8...