The current crisis of the city results from the fact that people seek the physical proximity of the urban effect, that suburbian developments put a heavy burden on the urban system as a whole. Forecasts say in 2000 half of the worlds population will live in agglomerations, that cover two percent of the planets surface using up three quarters of all natural resources. Still the same forecasters predict a doubling of the urban systems in energy needs.
Cities have to stay connected to the growth path to maintain their knowledge base. The availability of workers, services, suppliers makes it mandatory in an accelerating economy to stay close to the space of flows, as Manuel Castells has put it. The paradox phenomenon is that one one side this space of flows has expanded markets with modern transportation, logistics and communication technologies, and on the other side it created a new geography of power where the urban centers are increasingly important.