A megacity is a very large city, typically with a population of more than 10 million people.[1][2][3][4] The United Nations Department of Economic and Social Affairs (UN DESA) in its 2018 “World Urbanization Prospects” report defines megacities as urban agglomerations with over 10 million inhabitants.[5] A University of Bonn report holds that they are “usually defined as metropolitan areas with a total population of 10 million or more people”.[6] Elsewhere in other sources, from five to eight million is considered the minimum threshold, along with a population density of at least 2,000 per square kilometre.[7] The terms conurbation, metropolis, and metroplex are also applied to the latter.[7]
The total number of megacities in the world varies between different sources and their publication dates. The world had 33 according to UN DESA (in 2018), 25 according to the OCDE, 45 according to CityPopulation.de (in 2023), and 44 according to Demographia (in 2023). A good percentage of these urban agglomerations are in China and India. The other four countries with more than one megacity are Brazil, Japan, Pakistan, and the United States. African megacities are present in Nigeria, Egypt, South Africa, Angola and the DRC; European megacities are present in Russia, France, the United Kingdom, and Turkey (also in Asia); megacities can be found in Latin America in the countries of Brazil, Mexico, Colombia, Peru, and Argentina.
Some sources identify the Greater Tokyo Area as the largest megacity in the world,[5][8] while some others give the title to the Pearl River Delta in China.[9][10][11]