Joel Kotkin, author of the new Manhattan Institute Study, "America's Growth Corridors: The Key to National Revival," identifies four regions in the United States where a combination of low housing costs, above average population growth and business-friendly government can restart the American growth engine.  He says that future economic growth is not likely to be concentrated in the Northeast and California, but rather in less dense, more affordable, and markedly more pro-business growth corridors over the next 40 years.  Kotkin writes the weekly "New Geographer" column for www.Forbes.com.