For each letter of the alphabet, what is the most populous city in the world starting with that letter? [Use only the names the cities are usually known by in the English speaking world]

http://www.citypopulation.de/World.html

Ahmadabad
Buenos Aires
Cairo
Delhi
Edmonton
Fortaleza
Guadalajara
Hong Kong
Istanbul
Jakarta
Karachi
Lagos
Mumbai
New York
Oran
Paris
Qiqihar
Rio
Shanghai
Tokyo
Ufa
Vancouver
Washington
Xuzhou
Yekaterinburg
Zurich

And that lot took a bit of finding.

I have noticed, when researching population statistics, that there are wildly divergent numbers being used by various sources. This website, which cites UN population statistics, lists both Seoul and Sao Paulo as "S" cities that have a greater population than Shanghai:

http://www.citymayors.com/features/largest_cities1.html

But other websites list Shanghai as being the world's most populous city. See, e.g., :

http://www.infoplease.com/ipa/A0762524.html

My guess is that a lot of countries just don't have a thorough, accurate census that can be referenced with authority.

The Guinness Book of Records (when it was a proper reference book) used the total urban agglomeration when it claimed Mexico City as the world's most populous city. This may cause local grievances (such as Birmingham, UK including the Black Country) but it is the most sensible way to get comparable statistics for world city population figures.
I therefore award RMG a well-earned yay for his answer. The site he gives has some controversial English names. Taking these into account to give options where necessary and using RMG's list, I make it:

Ahmahabad, Bombay/Buenos Aires, Calcutta, Delhi/Djakarta, Edmonton/Ekaterinburg, Fortaleza, Guadalajara, Hong Kong, Istanbul, Jakarta/Johannesberg, Karachi, Los Angeles, Mexico City, New York, Osaka, Paris, Quito, Rio de Janeiro, Seoul, Tokyo, Urumqi, Vancouver, Washington, Xuzhou/Xian, Yekaterinberg/Yangon, Zhangzhou.

Some look undisputable and guessable enough to use in quizzes don't they?