ancient cities

864 Urban Ecology (Chicago School)
the most accessible site in the city, the central business
district became the most expensive land, and
land values decreased as a function of distance
from the center. Furthermore, the most valuable
land attracted those activities with the greatest
demand and the greatest cost. As the population
increases, the demand for central land intensifies,
and the areas of the city became more differentiated.
As population increases, the demand for
services increases and the price of the land located
at the center rises in order to accommodate the
increased demand. As the central commercial district
begins to expand outward, property owners
hold their residential property for resale to potential
employment users at a higher price that can be
obtained from residential users. Because commercial
users are paying for the land, the owners allow
their residential structure to deteriorate, creating
the zone of transition. Over time, the concentric
distributions start expanding to the fringes, and
natural areas experience a process of invasion,
competition, and succession.
Natural Areas
A major research effort of urban ecology is to
understand the process of formation and change in
natural areas. A natural area involves a geographic
area physically distinguishable from other adjacent
areas, a population with a unique social, demographic,
or ethnic composition and a social system
of rules, norms, and recurring patterns of social
interaction that function as mechanisms of social
control. Natural areas result from the different
kinds of land use and the varied populations that
occupy the city and are distinguishable areas of the
city with a particular culture and patterns of behavior.
Some common examples of these specialized
areas include the central business district, exclusive
residential areas, and areas of heavy or light industry,
immigrant communities, and poor neighborhoods.
These natural areas are the products of
ecological forces that work to distribute the city
population. Those who can afford the price of land
sort themselves away from functions or elements
that they regard as different. Each area, whatever
its function and population, is characterized by its
own moral code, which corresponds to the interests
and tastes of those who use it and what they use,
whether for residential, commercial, or recreational
purposes. Specific cultural values, social norms,
and codes of behavior can be identified in each
natural area.
The concept of neighborhood as a “natural
area” is a basic contribution of urban ecology and
the Chicago School to the sociological study of the
city and society. Change in the local population
composition is a major mechanism by which natural
areas change. The terms invasion and succession
were taken from plant and animal ecology,
and used to describe the process of neighborhood
population change. Competition, conflict, and
accommodation are viewed as natural processes
that characterize the relationships among different
populations. From this perspective the invasion of
a natural area by socially or racially different individuals
is met with resistance. Competition for
housing may be turned into conflict, as the locals
and the newcomers attempt to devise strategies to
best each other. If some accommodation between
the two populations is not reached, one of the two
groups will withdraw. If the newcomers withdraw,
the invasion has been halted. If the established
population withdraws, their departure, coupled
with the continued arrival of the new groups, will
result in succession, both of population and social
institutions.
Urban Spatial Structure
and Social Problems
Urban ecologists used the framework of population
distribution and change to study social problems.
They attempted to discover the processes by
which the biotic balance and the social equilibrium
are maintained once they are achieved and
the processes by which the biotic balance and the
social equilibrium are disturbed. Theories of
urban ecology were used as the basis for the study
of the distribution of delinquency and mental
health in the city, that is, the interrelationship
between population spatial distribution and the
distribution of social problems. Shaw analyzed the
characteristics of natural areas that, according to
the police and court records, had the most delinquents.
In these studies, a series of spot maps,
which pinpointed the residences of those juveniles
involved in various stages of the criminal justice
system, were presented. (Other spot maps showed
various other community characteristics, such as