A megacity is an urban area with a population of over ten million people. In 1975 there were only four megacities – New York, Tokyo, Mexico City and São Paolo. Today, there are over twenty. By 2014 less developed regions hosted the majority of the world’s megacities.
Distribution of the urban population by size class of urban settlement and number of cities
by development group, 1970, 2014 and 2030 – source – UN https://esa.un.org/unpd/wup/Publications/Files/WUP2014-Report.pdf
According to the UN by 2030, 13 new megacities are expected to emerge in the less developed regions: Ahmadabad, Bangalore, Chennai, Hyderabad (India), Bangkok (Thailand), Bogota (Columbia), Chengdu (China), Dar es Salaam (United Republic of Tanzania), Johannesburg (South Africa), Lahore (Pakistan), Lima (Peru), Luanda (Angola), and Thành Pho Ho Chí Minh (Vietnam).