The United Nations uses three definitions for what constitutes a city, as not all cities in all jurisdictions are classified using the same criteria.
The largest city by population using the city proper definition, which is the area under the administrative boundaries of a local government, is Chongqing, China.
The largest city by population using the metropolitan area definition, which is a loose term referring to an urban area and its primary commuter areas, is Tokyo, Japan.
The largest city by population using the urban area definition, which is a loose term referring to a contiguous area with a certain population density, is also Tokyo, Japan
There are 81 cities with a population of over 5 million people according to the United Nations 2018 estimates.