Historically, city-dwellers have been a small proportion of humanity overall, but following two centuries of unprecedented and rapid urbanization, roughly half of the world population now lives in cities, which has had profound consequences for global sustainability. Present-day cities usually form the core of larger metropolitan areas and urban areas—creating numerous commuters traveling towards city centers for employment, entertainment, and edification. However, in a world of intensifying globalization, all cities are in different degree also connected globally beyond these regions.
The most populated city proper is Shanghai while the most populous metropolitan areas are the Greater Tokyo Area, the Shanghai area, and Jabodetabek (Jakarta). The cities of Faiyum, Damascus, and Varanasi are among those laying claim to longest continual inhabitation.
A city is distinguished from other human settlements by its relatively great size, but also by its functions and its special symbolic status, which may be conferred by a central authority. The term can also refer either to the physical streets and buildings of the city or to the collection of people who dwell there, and can be used in a general sense to mean urban rather than rural territory.
A variety of definitions, invoking population, population density, number of dwellings, economic function, and infrastructure, are used in national censuses to classify populations as urban. Common population definitions for a city range between 1,500 and 50,000 people, with most U.S. states using a minimum between 1,500 and 5000 inhabitants. However, some jurisdictions set no such minimums. In the United Kingdom, city status is awarded on local criteria. According to the "functional definition" a city is not distinguished by size alone, but also by the role it plays within a larger political context. Cities serve as administrative, commercial, religious, and cultural hubs for their larger surrounding areas. Examples of settlements called city which may not meet any of the traditional criteria to be named such include Broad Top City, Pennsylvania (pop 452) and City Dulas, Anglesey, a hamlet.
The presence of a literate elite is sometimes included in the definition. A typical city has professional administrators, regulations, and some form of taxation (food and other necessities or means to trade for them) to feed the government workers. (This arrangement contrasts with the more typically horizontal relationships in a tribe or village accomplishing common goals through informal agreements between neighbors, or through leadership of a chief.) The governments may be based on heredity, religion, military power, work projects such as canal building, food distribution, land ownership, agriculture, commerce, manufacturing, finance, or a combination of these. Societies that live in cities are often called civilizations.