How polycentric are our cities ?

Today’s large metropolitan areas, from New York and London to Singapore and Tokyo, all comprise a multitude of interconnected centers: places, where our daily activities for employment, leisure and travel are highly concentrated. A deep and quantitative understanding of this urban spatial structure is of considerable importance for our contemporary sprawling cities, where it is ever-less obvious what constitutes a center. As an example, being able to predict how a new business hub interacts with already existing centers, and eventually changes the city-wide mobility patterns, is a prerequisite for developing efficient measures against traffic congestion and air pollution. The recent availability of many new, large-scale data from human activities, such as those automatically collected from mobile phone networks, opens now unprecedented possibilities to shed light on the increasing coexistence of multiple centers, offering numerous new applications for urban planning, infrastructural investments and environmental impact mitigation.