A new book Megapolitan America details this urban geography. It predicts that by 2040, there will be 10 distinct clusters composed of 23 megapolitan areas in the contiguous 48 states.

The authors define megapolitans as having at least one metropolitan area of 2 million people by 2040 that's connected — via commuting patterns — to at least one other metro area of more than 250,000 people. A megapolitan cluster has several megapolitan areas that are connected by commuting, trucking or commuter airline and share terrain, climate, culture, economic base and political culture.
Published by APA Planners Press