OpenStreetMap is a wiki style map of the entire world.  It has a flexible key/value tagging system that allows the data in it to evolve relatively easily.  This flexibility has allowed it to be used in everything from disaster response to micro-mapping of locations such as zoos and parks.  There are lots of examples of historical sites mapped within OSM.  One local to the Washington D.C. area is Arlington National Cemetery.

In other areas there have been efforts to create maps from OpenStreetMap data towns at various snapshots in time.  This is done by utilizing begin and end date tags for buildings.  That way if you render a map for the year 1840 for example only those buildings standing during that time while be displayed.  Frankie Roberto has an interesting series of slides showing this idea of start and end attributes in OpenStreetMap.

When I asked on one of the OSM community mailing lists for examples of sites of historical significance in OpenStreetMap I received many responses.  I’m interested in discussing this application of the project as well as potentially others of interest to the digital humanities.