Get lost in map data: Policymap
After the Where 2.0 conference, I had a chance to catch up a bit with Jaron Waldman, the CEO of Placebase, which makes the demo site Pushpin that I covered from the conference. He had another demo to show me, but this one is a bit more useful: PolicyMap.
Made for Placebase customer The Reinvestment Fund, it's a collection of real estate, civil, and financial built into a mapping and charting engine. It can locate superfund sites; show you crime stats; tell you about mortgage originations (including things like subprime mortgages to various demographic groups), and age and educational background. The data is at a variety of resolutions (some is per ZIP code, some by census tract) and timeliness (census data, obviously, is only current up to 2000).
PolicyMap can drill deep into demographic information. This image shows unemployment stats from a four-square-block area.
In many data sets you zoom into deep detail on your information. You can also build charts, for data sets with information over time, and generate pre-configured "community reports" for particular regions or any areas you define.
It's a lot of data.
Unfortunately, despite all of the data and all the options to display it, a few useful views are missing. For example, while you can easily see the percentage of people per census tract within a certain age range (such as 18 to 34), there's no report that I found that can help you visualize average age. And here's a tip: Don't press the back button to try to undo a mapping step; it doesn't work as you expect and will just get you lost.
PolicyMap is free to use for public data. Some data sets, such as home sale statistics, require a paid membership, for $200 a month.
See also: Cyberhomes, Zillow, Trulia, and Swivel (BYO Data)
Rafe Needleman writes about start-ups, new technologies, and Web 2.0 products, as editor of CNET's Webware. E-mail Rafe. 
