World's largest cities

Determining the world's largest cities depends on which definitions of city are used. The United Nations uses three definitions for what constitutes a city, as not all cities may be classified using the same criteria. Cities may be defined by the extent of their urban area, the metropolitan region, and the city proper.

Common methods for defining the boundaries of a city

Urban areas

A city can be defined as a conditionally contiguous urban area, without regard to territorial or other boundaries inside an urban area. UNICEF defines urban area as follows:

Metropolitan area

A city can be defined by the habits of its demographic population, as by metropolitan area, labour market area, or similar in a metropolitan area. UNICEF defines metropolitan area as follows:

City proper (administrative)

A city can be defined by its administrative boundaries (city proper). World Urbanization Prospects, a UN publication, defines population of a city proper as "the population living within the administrative boundaries of a city or controlled directly from the city by a single authority." UNICEF defines city proper as "the population living within the administrative boundaries of a city, e.g., Washington, D.C.". A city proper is a locality defined according to legal or political boundaries and an administratively recognised urban status that is usually characterised by some form of local government. Cities proper and their boundaries and population data may not include suburbs.