You're an urban planner, looking at a tabletop model of a city. You would like to know what the impact would be if a proposed new building were moved to the left, so you shift it slightly. A digital shadow appears from the base of the building, a high-speed wind tunnel is generated and the reflection off the glass building blinds motorists driving by-evidence that perhaps the change wouldn't be such a good idea after all.

Developed under the direction of Hiroshi Ishii at MIT's Media Lab, this urban simulation uses a specially designed lightbulb with a built-in camera and projector to track the position of buildings in a model. The camera recognizes the structures using an optical tagging system; small colored dots encode the object's dimensions. When a structure is moved, the system displays the resulting shadows and wind patterns on the model's surface. Developers in Boston and Washington, D.C. have already expressed interest in using the system for their construction projects.