This is a list of the most populous cities in the world, defined based on 2018 United Nations estimates, official census estimates, and the 2021 "Demographia World Urban Areas" report.
"World Urbanization Prospects," a publication by theONU, defines the population of a real city as "the population living within the administrative boundaries of a city." For many of the metropolises, however, the metropolitan area is administratively distinct from the urban agglomeration proper. For this reason, ONU recent estimates distinguish three definitions of cities: cities proper, urban areas and metropolitan areas.
According to the definition of "city proper", based on administrative uniqueness, the Chinese city of Chongqing is the largest in the world.
According to the other two definitions, Tokyo, despite being divided into several administrative units, is the most populous "urban agglomeration" (i.e. the agglomeration without rural areas) in the world, while the Chinese city of Shanghai is the most populous "metropolitan city" (i.e. the area interconnected by common infrastructure and frequent transport).
The data in this gallery include the total population of agglomerations in their highest estimates, thus also including metropolitan areas.