You have to opt-in to be shown by name, but anonymous usage is shown by default: MIT uses management information from the 2,800 access points on campus to pinpoint user locations in 3D. (The article says "log files" and "university's ISP," but it's almost certainly SNMP and the IT department.)
The maps are being shown in real time at the MIT Museum. Background information is online at ispots.mit.edu.