Massive, sprawling cities are a hallmark of the cyberpunk genre, hell, Gibson’s defining series was called the “Sprawl Trilogy”.
Well, I found this rather useful wikipedia page for figuring out where exactly to place your futuristic metropolis. It shows the regions of the world where urban megapolises are currently developing. Useful, especially for those of use that don’t come from those countries and have no idea, beyond what you’ve seen in movies.
I really need to name one city “The Golden Banana”, heh. 😀