The concepts of 'megalopolis' and 'exopolis' describe distinct but sometimes overlapping phenomena in urban growth and development.

Megalopolis was a term coined by Jean Gottmann in 1961 to describe the vast, sprawling urban region along the northeastern seaboard of the United States, stretching from Boston to Washington D.C. (often called 'BosWash'). A megalopolis is characterized by the coalescence of several large metropolitan areas, forming a continuous, highly urbanized corridor that can extend for hundreds of miles. It is a super-metropolitan region with a high population density, interconnected economic and social systems, and shared infrastructure. Other examples include the Tokaido corridor in Japan and parts of the European 'Blue Banana' region. The defining feature is the physical and functional merging of multiple urban centers into a single, massive urbanized zone.

Exopolis, a term introduced by Edward Soja, describes a city or urban area that is 'outside' the traditional urban core, often characterized by a fragmented, decentralized, and sprawling landscape. It represents a post-modern urban form, typically lacking a single, dominant center and instead comprising multiple edge cities, suburban employment centers, and residential areas. Exopolises are often car-dependent, characterized by a blurring of urban-rural boundaries, and associated with globalized capital flows and social polarization. Los Angeles is frequently cited as a prime example of an exopolis, with its polycentric structure and vast suburbanization.

Overlap: Yes, megalopolises and exopolises can and often do overlap. A megalopolis describes a large-scale regional phenomenon of urban coalescence, while an exopolis describes a type of urban form or process of urban restructuring that can occur within or contribute to a megalopolis. Many of the individual metropolitan areas that constitute a megalopolis might exhibit exopolitan characteristics, especially in their newer growth areas, outer fringes, or sprawling suburban developments. For instance, within the BosWash megalopolis, many of the suburban and exurban areas, with their decentralized employment and residential patterns, can be described as exopolitan. The exopolis represents a process of decentralization and fragmentation that can occur within the broader spatial extent of a megalopolis, contributing to its overall sprawling and polycentric nature.