When people wander around the MIT campus with a Wi-Fi-enabled cell phone or laptop, they're also participating in a real-time mapping project. Carlo Ratti, a practicing architect with a firm in Torino, Italy, runs the SENSEable City Laboratory in the university's department of urban studies and planning. He can reveal patterns of activity on the MIT wireless network, which blankets almost the entire campus, by measuring activity on wireless access points. Technology Review. Previously @ TR:1 and 2