Which city has the most taxis in the world? How many does it have? (Please cite your source.)

Mexico city with 60.000

Source
http://facts.330.ca/world/

I found about 10 sites referring to these figures.

That's it, Jenny. The reason I asked for a source was to eliminate a trivia-type source, which have so many errors. Even the one you provided has the following:

"The Amazon is the world's largest river, 3,890 miles (6,259 km) long."
I don't know what they mean by "largest river" but since they only mention its length, one must assume that is what they mean. They are wrong. The Nile, at 4180miles (6690 km) is longer. Had they said that the Amazon has the greatest discharge, they would have been right.

"Sweden has the lowest birth rate (1 in 100)."
I assume that they mean lowest of any country, but the birth rate for the Vatican City is zero per 100. If you doubt that the Vatican City is a country, just scroll down on the site to where it states, erroneously, that "Vatican City is the smallest country in the world, with a population of 1000 and a size 108.7 acres."

"Donald Duck Comics were once banned in Finland because he doesn't wear pants."
Completely untrue. The mix-up stems from the fact that Donald Duck comics were included in a government funded program for children, and one politician complained that money was spent buying children comic books.

These are just the ones I know are wrong. There are a few I suspect are wrong, but have never checked.

I have seen Mexico City named as the city with the most taxis in the world many times, but always on a trivia-type site, and wanted something more authoritative. My source was the Jackson County (Oregon)Library Services, who, in their monthly newsletter, had a book review of Mathew Todd Rosenberg’s The Handy Geography Answer Book was published in 1999.
"("Congested Mexico City is home to more than 60,000 taxis among its 3.5 million automobiles.”)"