What is the world's largest urban sprawl?

What is the main reason for urban sprawl?

It has to be the L.A. area. You've more than 10 million, or many more, people spread out to the max. Some sources say Chicago is larger, which is absurd. Chicago has fewer people in every regard, and more tall buildings, certainly proportionally, which makes it logically impossible to be bigger in two regards.

NYC can't be larger as well, which some claim it is, but probably mean population wise. NYC is built taller, which makes it impossible to be larger, i.e. wider than L.A. The NY area overall is probably several stories taller than LA, so if it were even as expansive as LA it would have had to have several times LA's population, which it far from does.