As a system of social organization: Cities have a characteristic social structure, a series of social institutions and a typical pattern of social relationships. Wirth had identified the following major effects upon human association and social life in communities that are typically large and whose population is dense and socially heterogeneous.

Firstly, increase of individual variation in the population. Level of differentiation is greater in the cities. The personal traits, the occupations, the cultural life, and the ideas of the members of an urban community are expected to range between more widely separated poles than those of rural inhabitants. He contrasts such bonds with that of folk society. Instead of competition and formal control mechanism, in folk society we have bonds of solidarity.

Secondly, large numbers contribute to the segregation of population groupings. City dwellers are also dependent on more people for the satisfactions of their life needs than are rural people and thus are associated with a greater number of organized groups. At the same time, they are less dependent upon particular persons. In other words, the city is characterized by secondary rather than primary contacts.