mikemuch writes "Imran Haque has developed a mashup of Google Earth with data from the U.S. Census Bureau, called gCensus. The app uses the XML format known as KML (Keyhole Markup Language), which can create shapes and colors on the maps displayed by GE. Haque had to build custom code libraries (which he's made available as open source) that could generate KML for the project. He also had to extract the relevant data from the highly counter-intuitive Census Bureau files and store them in a database that could handle geographic data. gCensus lets you do stuff like create colorful overlays on maps showing population ages, race, and family size distributions."