Photo by Anne Roberts.

Size and density are influential in determining the livability of a city. Photo by Magalie L'Abbé.

What will a world population of 7 billion do to our quality of life? Photo by the World Resources Institute.

The 2010 U.S. Census reveals an interesting juxtaposition between a young minority population and a maturing white population. Photo by Owls Flight Photography.

Although already at 11 million residents, Tianjin is expected to see a surge in population by 2030. Photo by Bill Benson

Click on the above image to watch Geoffrey West's TED talk.