Architects and urban planners have long debated the idea that built environments can positively affect social behavior. It's always been easier to argue for the opposite position, that ill-conceived buildings can foster anti-social behavior. Richard Sennett proposes that properly designed public spaces can enhance cooperation. The lecture is in reference to his new book, Together: The Rituals, Pleasures, and Politics of Cooperation.
For other views on this topic, see Michael Chen's essay on networks and architecture, as well as Ethel Baraona Pohl's look at the Plaza de la Encarnación in Seville, Spain, a site for the Movimiento 15M.