How 4 Million Commutes Shape America's 'Megaregions'

Cities have “limits,” drawn to mark populations and bound services, but they are porous as scrim. Cars, cash, freight, and natural resources flow readily between neighboring jurisdictions, following the market more than any lines on a map.

Multiple metros glued together in this way—think of the Northeast Corridor or “Char-lanta”—are sometimes called a “megaregion.” Far from a euphemism for unbridled sprawl, megaregions have become an important framework for developing projects that serve boundary-crossing populations, like high-speed rail or key environmental protections.