The Scaling of Human Interactions with City Size

The pace of life accelerates with city size, manifested in a per capita increase of almost all socioeconomic rates such as GDP, wages, violent crime or the transmission of certain contagious diseases. Here, we show that the structure and dynamics of the underlying network of human interactions provides a possible unifying mechanism for the origin of these pervasive regularities. By analyzing billions of anonymized call records from two European countries we find that human social interactions follow a superlinear scale-invariant relationship with city population size. This systematic acceleration of the interaction intensity takes place within specific constraints of social grouping. Together, these results provide a general microscopic basis for a deeper understanding of cities as co-located social networks in space and time, and of the emergent urban socioeconomic processes that characterize complex human societies.