Historical Chinese geographical data
The Chinese Historical Geography database project, based at Harvard University, offers a mind-boggling array of historical geographical information in GIS format.
It includes more than 45 layers of data covering: Prefecture Capitals, County Capitals, Towns and Villages, County Boundaries, Prefectural Boundaries, Province Boundaries, Rivers, Lakes, Historical Coastline, Topographic Background Images, administrative hierarchy table, source notes, and numerous other GIS layers. These datasets are available for free download from the CHGIS website, and can be searched online using the CHGIS search engine. They do require GIS software to view. Some free GIS programs are available (see http://www.fas.harvard.edu/~chgis/data/chgis/downloads/v4/ for software details and http://www.sli.unimelb.edu.au/gisweb/ for a beginning GIS tutorial.)
This is a pretty amazing tool for anyone who wants to really envision China's history!