World's largest cities

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The question of which are the world's largest cities does not admit of a single, simple answer. It depends on which definition of a city is used, and how that definition is applied to complex facts on the ground. Debate on this field is highly vulnerable to manipulation, as people tend to prefer whichever definition flatters their own city most.

The "size" of a city can refer to either its physical extent or, more typically, its population. Furthermore, there are three main ways of delineating the boundaries of a city:

• A morphological definition based on the urban area, which is usually defined as the continuous built-up area with the maximum allowable gap between structures of typically 200 m. The delineation is usually done using population density criteria, or by satellite/aerial maps, without regard to political boundaries. For statistical convenience, such areas are sometimes adjusted to appropriate administrative limits, sometimes including rural areas within the adjusted boundaries (urban agglomeration).

Main articles: List of urban areas by population and List of urban agglomerations by population

• A functional definition based on the concept of a metropolitan area or labor market area. This definition is usually based on commuting from home to work. Commuter flow thresholds into the core urban area are established by the national census authority to determine which areas are included or not in the metropolitan area.

Main article: List of metropolitan areas by population

• An administrative definition, typically based on a municipality (city proper) or equivalent entity, or sometimes a group of municipalities under a regional government.

Main articles: List of cities proper by population and List of cities by surface area

All of the above, and any other list, should be seen as interpretations, rather than hard fact.