Certainly sustained economic growth, low density and more affordable housing all clearly continue to push the center of population gravity toward certain Sun Belt cities, primarily in the Southeast and Texas.

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Opponents point out that unlike areas in other countries, mass transit is only economic viable in areas with sufficient density and that on a large scale, massive public transit programs have no chance of becoming self-sufficient.

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The risk of loss of lives and economic disaster in the southern Mediterranean is high due to strong population density along its coasts: around 150 million people concentrated in 46, 000 kms of coastline, 110 million of them living in cities bordering the sea and some 200 million tourists visiting the area every year.

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Indeed, smaller, low-density Des Moines nearly broke into the top 10 (13th), reflective of the economic gains being made in the Great Plains.

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