allowed for the production of an agricultural surplus, which in turn led to a differ-
entiation of labor, development of social classes, and the emergence of more
sophisticated economic and political systems than had previously been the case.
The morphology of many early cities was haphazard and chaotic, but some urban
areas in the ancient world were surprisingly organized and well planned. The city
of Mohenjo Daro, established around 2500 BCE in the Indus River Valley, was
clearly a planned settlement with streets and buildings constructed following a
grid system, covered sewers, and a municipal garbage collection system! But in
general, cities for much of history were places of squalor, congestion, and disease
until the late 19th century. Pestilence typically spread quickly in urban areas, due
to high population densities and poor sanitation. Industrialization and theagricul-
tural revolutionthat accompanied it initiated a surge in urbanization that contin-
ues in many parts of the world, as thousands of rural workers migrated to the cities
seeking employment. By the mid-20th century, zoning legislation,urban decen-
tralization, the development ofgreen belts, and other factors had lowered popu-
lation densities and improved the quality of life in many urban areas in
developed countries, while large cities in the developing world continued to strug-
gle with the problems of pollution, overburdened transportation networks, and
shortages of adequate housing and basic services.
The process of urbanization may be driven by numerous forces. The population
of urban areas may grow via a relatively high rate of natural increase, or by the
arrival of migrants from other regions.The qualities of the physical landscape
may coincide with the presence of abreak-of-bulk point, or trade flows may lead
Urbanization 351Edge Cities
One of the newest concepts in the study of urban geography in the developed world is the
edge city. Edge cities arise along the margin of major metropolitan areas, especially at the
juncture of interstate highways, or they may be planned as independent suburban hubs, and
in many cases are near large airports. They frequently are characterized by the presence of
office parks, shopping malls, relocated corporate headquarters, and more green space than
is found in the typical Central Business District. In addition, they are built for easy and quick
access by automobile and did not appear on the urbanlandscapeuntil the advent of the
car as a major means of transport. The quintessential description of the emerging geography
of the edge city is Joel Garreau’sEdge City: Life on the New Frontier, the first book-length study
devoted to the phenomenon. Garreau provides a typology of edge cities, as well as identifying
the characteristics that uniquely distinguish this form of urban development. Edge cities have
become a common element of the urban landscape in America, and to a lesser degree in
other developed countries, indicating the dynamic nature of the modern cityscape in the
information era.