A map of Mexico City, created in 1550 and thought to be the work of Spanish cosmographer Alonso de Santa Cruz, is available for viewing. As well as being able to navigate and zoom about the map, registered users can also annotate locations, adding in pieces of background information to enable the map to become more understandable. The map is one of only two such maps from the time period that depicts Mexico City and is painted on parchment.

By way of Geospatial Semantic Web Blog