The 9th edition of the National Geographic Atlas of the World, published in 2011, estimated the urban area population of the world's largest cities, those with a population above 10 million people, which they termed "megacities." The population estimates for the world's largest cities below are based on population estimates from 2007.
Population numbers for the world's largest cities are rounded since they are incredibly difficult to determine precisely; millions within most megacities live in poverty in shantytowns or other areas where accurate census taking is near impossible.
The following eighteen largest cities in the world are all those with a population of 11 million or more, based on the National Geographic atlas data.
1. Tokyo, Japan - 35.7 million
2. Mexico City, Mexico - 19 million (tie)
2. Mumbai, India - 19 million (tie)
2. New York City, United States - 19 million (tie)
5. Sao Paulo, Brazil - 18.8 million
6. Delhi, India - 15.9 million
7. Shanghai, China - 15 million
8. Kolkata, India - 14.8 million
9. Dhaka, Bangladesh - 13.5 million
10. Jakarta, Indonesia - 13.2 million
11. Los Angeles, United States - 12.5 million
12. Buenos Aires, Argentina - 12.3 million
13. Karachi, Pakistan - 12.1 million
14. Cairo, Egypt - 11.9 million
15. Rio de Janeiro, Brazil - 11.7 million
16. Osaka-Kobe, Japan - 11.3 million
17. Manila, Philippines - 11.1 million (tie)
17. Beijing, China - 11.1 million (tie)
Additional lists of population estimates for the largest cities in the world can be found in my Largest Cities of the World collection of lists.