to the emergence of anentrepoˆt, either of which may stimulate economic opportu-
nities and urban growth. This in turn will lead to a higher demand for labor, attract-
ing immigrants seeking employment opportunities. Subsequently, urbanization is
compounded by the effects ofagglomeration, which increase the scale of economic
development and bring additional residents to the urban place. A classic example of
this process is the growth of Chicago’s population (along with other cities in the
northernregionof the United States) between 1910 and 1930, when hundreds of
thousands of African Americans migrated from the American South to the indus-
trial urban centers of the Midwest. The desire to escape discrimination in their home
states drove many of these migrants northward, but the most important factor
behind this movement was economic expansion in the north, resulting in the crea-
tion of tens of thousands of jobs. Chicago’s black population expanded by nearly
200,000 in these 20 years, or an increase of almost five times the figure of 1910.
This domesticmigrationof American blacks to northern cities followed decades
of immigration to those locations by Europeans, who mostly came seeking the
economic advantages such large, growing urban places offered.
Geographers have developed various models to describe the developmental
patterns of urbanization. Thepre-industrial city modelwas first articulated in the
work of Gideon Sjoberg in the early 1960s. Sjoberg held that prior to the industrial
age, social and political authority was concentrated in the center of the typical city,
and that many cities in the developing world continue to follow this pattern. In the
decades prior to Sjoberg’s work, urban geographers had offered several theoretical
perspectives on the spatial character of urban places, based on cities in the economi-
cally developed world. The first such effort was the concentric zone model, which
was based on the development of Chicago in the 1920s. In this case, the urban space
is divided into a series of rings around the Central Business District (CBD). Each
ring is characterized by a specific type of economic use and activity. In 1939 Homer
Hoyt presented a revised urban model, which became known as thesector model,
or sometimes simply the Hoyt model. The sector model emphasizes the role of
transportation linkages in the development of distinct urban functional zones,
resulting in “sectors” of development that are associated with transport access and
economic functionality. The multi-nuclei model, introduced after World War II,
attempts to incorporate some elements from the previous models, while also
accounting for the rise of extensive suburban development and other phenomena
of urbanization that had appeared by the mid-1940s. All of these models are some-
what flawed, but nevertheless have contributed to our understanding of urbanization
processes.
In the last decades of the 20th century, new trends in urbanization were identified,
serving to highlight the complexity of the urbanization process. The emergence
of so-called asylum suburbs is an example. In these locations residents live along352 Urbanization