More on the city of 7 billion

In a previous post I mentioned how the world's population could fit into France provided everyone lived in a city as a dense as Paris. I stumbled across this interesting blog, which takes the same notion but looks at the size of this mega city if it was based on different densities:

http://www.persquaremile.com/2011/01/18/if-the-worlds-population-lived-in-one-city/