Digitizing old maps is a rich field — take, for instance, the Foursquare-style check-in app for obsolete restaurants and bars or the treasure trove of online images posted by David Rumsey. But this mash-up, done by San Franciscan Shawn Clover, stands out. He's created two batches of images (part one is here) that merge post-earthquake San Francisco from 1906 with contemporary times — he studied old photos and then went out to try to recreate the shots from the same vantage point. The results are pretty seamless. Check out his blog for the full collection. Hat tip: @burritojustice, @jonvoss.