MICHAEL BARONE on the realignment of America: “It has become a commonplace to say that population has been flowing from the Snow Belt to the Sun Belt, from an industrially ailing East and Midwest to an economically vibrant West and South. But the actual picture of recent growth, as measured by the 2000 Census and the census estimates for 2006, is more complicated. Recently I looked at the census estimates for 50 metropolitan areas with more than one million people in 2006, where 54% of Americans live. . . . What I found is that you can separate them into four different categories, with different degrees and different sources of population growth or decline. And I found some interesting surprises.”