People living in big cities maintain a close network of social connections, and one that is larger than those in smaller urban areas.
A team led by Markus Schläpfer of the Massachusetts Institute of Technology in Cambridge used a database of billions of telephone calls from Portugal and the United Kingdom to measure social connectivity. They found that personal contacts are tightly clustered in cities of all sizes, suggesting that people form close-knit communities no matter where they live. But the number of contacts per person in big cities grew more than expected, the authors report. Residents of Lisbon had, over the course of 15 months, on average, 11 reciprocated mobile-phone contacts compared with the residents of the smaller Portuguese city of Lixa, who had six.
The authors suggest that networks of human interaction underlie the systematic acceleration of urban growth.