Using the 1500 map of Venice by Jacopo de'Barbari, this project allows you to compare the old city of the map with modern line drawings and ariel views. There is also an image database of Venetian art in situ.
You can search for the monuments themselves or for post-Antique Documents. Entries for each work give images of the work, details about it, and documentation from the Renaissance. References in other texts are given, and a link to Google Earth shows the exact location.