AMERICANS are more connected now than ever. Mobile phones allow people to maintain relationships with friends, family and colleagues across long distances.

If you analyze aggregated cellphone traffic — as researchers at M.I.T., AT&T and I.B.M. did with United States data from July of last year — interesting patterns emerge.

Cities become connective hubs as people move to them from nearby counties and from far across the country. As a result, many calls originate and end in cities, connecting urban citizens to their families back home.

At the same time, communities emerge that have little to do with geographic boundaries. While some follow state lines, others split states in half or combine them.