I hate to say something nice about Trulia so soon after plugging the site, but you absolutely have to check out a new Trulia feature called Hindsight, which dramatically and colorfully illustrates the birth of cities.
Choose a city and Trulia shows on a satellite image where houses were built each year. Each house is a dot, and each decade the dots are a different color. The animation zooms through the decades, with new houses exploding onto the map the year they’re constructed and then shrinking back to pinpoints. You can see the almost-overnight construction in Levittown, N.Y., after World War II. The deathly quiet of construction in Detroit in recent decades. The massive boom in Las Vegas. And of course you can put in your own home’s Zip code. (The image here is from Plano, Tex.)
Hindsight presumably doesn’t show homes that were built and later torn down, so it understates the amount of construction in the past. But that’s a quibble. Check it out! (Now that’s it—no more plugs for Trulia the rest of 2007.)