Source: adapted from H. Carter (1995) The Study of Urban Geography,
Fourth Edition, London: Arnold, p. 126. Sector and Nuclei Urban Land Use RepresentationsA study of residential areas done by Hoyt (1939) in the North American
context concluded that the land use pattern was not a random distribution,
nor sharply defined rectangular areas or concentric circles, but rather
sectors. Thus, the effect of direction and time was added to
the effect of distance. Transport corridors, such as rail lines,
public transit and
major roads, are mainly responsible for the creation of sectors, thus
transport has directional effect on land uses. Cities would grow along major axis. The sector representation also includes concentric
transitional processes observed by Burgess, which is occurring along
a specific direction.Following Hoyt's development of a sectorial city, Harris and Ullman
(1945) introduced a more effective generalization of urban land uses.
It was brought forward that many towns and nearly all large cities do
not grow around one CBD, but are formed by the progressive integration
of a number of separate nuclei in the urban spatial structure. These nodes
become specialized and differentiated in the growth process and are
not located in relation to any distance attribute, but are bound by
a number of factors:
Differential accessibility. Some activities require specialized
facilities such as port and rail terminals. For instance, the retailing
sector demands maximum accessibility, which is often different from
centrality offered in the CBD.
Land use compatibility. Similar activities group together
since proximity implies improved interactions through economies of agglomeration. Service activities such as banks,
insurance companies, stores and institutions are strongly interacting
with each other. This can be defined as centripetal forces between
activities.
Land use incompatibility. Some activities are repelling
each-other such as high quality residential and heavy industrial
areas.
This may be defined as centrifugal forces and one of the
main reasons why poorer neighborhoods tend to be located on the
eastern side, at least in industrial cities. Since in the
northern hemisphere, prevailing winds tend to be
westerlies,
so eastern sections of an industrial city tended to have a
higher level of exposure to industrial air pollution.
Location suitability. Some activities cannot afford the
rent of the optimal site for their location. They are thus locating
at cheaper places, which are not optimal, but suitable for these
activities.
Harris and Ullman poly-nuclear model was the first to represent the
fragmentation of urban areas, specialized functions as well as suburbanization.
