Zillow, the leader in house price and property data, released this great map of counties in the US with the percentage of house that are “underwater” (which have negative equity, or who’s owners owe more on their mortgage than the property is estimated to be worth).
The mortgage and financial data was supplied by TransUnion, house prices by Zillow, based on first quarter 2012 data.
It looks like the visualization was built using the Leaflet JavaScript library by CloudMade.
The interactive portions include typical zooming of the map, a nice zip/city/county search box, and a mouseover popup of details when moving the mouse over each county.
The U.S. Housing Crisis: Where are home loans underwater?
Visualization Central 