The study of the evolution of an urban system raises a number of
practical questions, as to the operational definition of the components
of the system as well as to the incorporation of the factor time in the
analysis. In this chapter the fo- cuss is on the urban centres, the
nodes of the urban system. One of the first pro- blems to be solved now
is the definition of such a node. It has been argued above that
population size can be used as an approximation of the complexity of the
spatial economic structure of a region. The acceptation of this notion
makes it possible to study the urban system as a population system. The
analysis of the population system over the study period will be pursued
from this perspective. The study period, 1840-1970, covers completely
the industrialization and urbanization phase which occurred during the
industrial revolution. Over this period the spatial organizational
structure of society evolved from a rural-commercial to- wards a modern
urban-industrial state. One of the major events in this period of change
is the spatial redistribution of the population and the population
growth. This process will be examined below at three levels of
aggregation: (I) the popu- lation distribution as one frequency
distribution, (2) the population distribution dis aggregated into a n
ber of size classes, and (3) the individual cities which make up the
population distribution.