This could be the most detailed open-data map of urban gerontology in existence; the Portland project used about half of the number of property records. It’s not a flawless diamond, though. Some of the dates are approximate or inaccurate.
Google Maps now features #BikeNYC lanes & directions! They’re not 100% perfect, but they are damn near close. If you’re part of the anti-google mafia, you should take a look at Ride the City. Not only were they first, but they use OpenStreet Maps. I can’t wait for Spokes iPhone app to include this data. (h/t @yaweneep)