I also love David Rumsey's collection! Check out the rumsey map center at Stanford if you ever find yourself in the area, it's ridiculously cool
Pastmaps was really born out of my desire for more advanced features, layers, and tools on rumsey's site and I'm hoping I can eventually deliver on that vision (spoilers: I'm definitely not there yet)
Pastmaps was really born out of my desire for more advanced features, layers, and tools on rumsey's site and I'm hoping I can eventually deliver on that vision (spoilers: I'm definitely not there yet)