Megacity: An metropolitan area with a population of more than 10+ million people. The population density is usually over 2,000 persons/km2.
Millionaire City: A city with over a million inhabitants.
World City: Big population. A city that acts as a major centre for finance, trade business, politics, culture, science, information gathering and diffusion, publishing and mass media, and all the associated activities - serving not just a country or a region but the whole world. New York, London and Tokyo are the three preeminent world cities although there are some others that could be considered 'important multinational cities'.
Urbanisation: The growth in the proportion of a country's population that lives in urban…