overpopulation is an issue that comes up every once and a while.
here are some facts all according to wikipedia
Land area of earth: 148,939,100 km²
Human population 2005: 6,453,628,000
Manhattan, NY pop. density: 25,849/km²
Land area of Oregon: 255,026 km²
You could put all of the people in the world into Oregon at the density of NYC and have the rest of the world untouched. All 148,684,074 km² of it.
We'd still have to flush our toilet on California, but they deserve it.