Dr. Mike Walden, North Carolina Cooperative Extension economist in the College of Agriculture and Life Sciences at N.C. State University, responds:

"Megacities are urbanized areas that may stretch over hundreds of miles. For example, some claim that there is a megacity that stretches from Boston to Washington. And also, there is a megacity, some say, that goes from Raleigh-Durham to Charlotte and Atlanta and all the way to Montgomery, Alabama. Now clearly, these are separate cities, separate municipalities, but the point is that they're linked, and that a lot of the area between those cities is rapidly urbanized. And these researchers say that these megacities are really the true economic engines of our modern world, and you think of megacities instead of states or instead of even nations. And so when you calculate how important economically some of these megacities are, it's very impressive. For example, it's estimated that the megacity stretching from Boston to Washington - which some call Boswash - produces $2.2 trillion of economic output each year. And the megacity that goes from Raleigh to Montgomery, Alabama is responsible for over $700 billion of economic output each year. So megacities may be the economic geography of the future."