There is considerable confusion in both Chinese and foreign sources over definitions of urban places and hence considerable variation in estimates of China's urban population (see Migration in China). The problem of determining the size of the urban population reflects inconsistent and changing administrative categories; the distinction between rural and urban household registry and between categories of settlements; the practice of placing suburban or rural districts under the administration of municipal governments; and the differences in the status accorded to small towns. In sociological terms, urban refers to an area characterized by a relatively high degree of specialization in occupational roles, many special-purpose institutions, and uniform treatment of people in impersonal settings. In this sense, a Chinese market town is more urban than a village, and settlements become more urban as they grow in size and economic complexity. Municipalities like Beijing and Shanghai have the highest degree of division of labor and the most specialized institutions. Distinctive features Legal status as an urban dweller in China is prized. As a result of various state policies and practices, contemporary Chinese urban society has a distinctive character, and life in Chinese cities differs in many ways from that in cities in otherwise comparable developing societies. The most consequential policies have been the household registration system, the legal barriers to migration, the fostering of the all-embracing work unit, and the restriction of commerce and markets, including the housing market. In many ways, the weight of official control and supervision is felt more in the cities, whose administrators are concerned with controlling the population and do so through a dual administrative hierarchy. The two principles on which these control structures are based are locality and occupation. Household registers are maintained by the police, whose presence is much stronger in the cities than in the countryside (see Public Security Bureau). Cities have been subdivided into districts, wards, and finally into small units of some fifteen to thirty households, such as all those in one apartment building or on a small lane. For those employed in large organizations, the work unit either is coterminous with the residential unit or takes precedence over it; for those employed in small collective enterprises or neighborhood shops, the residential committee is their unit of registration and provides a range of services. The control of housing by work units and local governments and the absence of a housing market have led