Image Credit Per Square Mile
@stevemouzon tweets about Per Square Mile, which graphically demonstrates how much space all the people in the world would take up if they were packed as tightly as they are in Paris (three states) to Houston (well over half of the States) but even at Houston densities, there is a lot of world left empty. See more here.
U.S. not dense enough for high-speed rail? Think again
The site is full of interesting presentations of data. Tim De Chant writes about his one:
Low population densities are often cited as the reason why high-speed rail would never work in the United States. While it's true that typical American metropolitan areas sprawl far and wide, many larger cities are still relatively dense, and a surprising number of our states are as dense as some European nations.