Building Historical Maps
Amherst College are working on a mapping project called Cityscapes. Cityscapes is a tool to allow students to collaborate in their studies. I think the idea of the project is to create an application that students can use to easily add markers, photos, videos and other content to a shared Google Map.
Currently there are two working demos of the project:
The two demos allow you to overlay historical maps of Tokyo and Paris on top of Google Maps. The Tokyo demo is supposedly password protected, for copyright reasons, but I found just pressing cancel on the log-in worked for me ;)