https://en.wikipedia.org/wiki/Megacity#Growth
1920 Tokyo: 3.7 million[1]
1950 Shanghai: 6.2 million[2]
1971 Mumbai: 5.9 million[3]
1921 Greater London: 7.5 million[4]; Inner London: 4.9 million
Terms like Metro-area and Megalopois are different stories...
[0]https://www1.nyc.gov/site/planning/data-maps/nyc-population/...
[1]http://www.metro.tokyo.jp/ENGLISH/ABOUT/HISTORY/history03.ht...
[2]https://en.wikipedia.org/wiki/Demographics_of_Shanghai
[3]https://en.wikipedia.org/wiki/Mumbai#Demographics
[4]https://en.wikipedia.org/wiki/Demography_of_London
https://en.wikipedia.org/wiki/Megacity#Growth