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CELLULAR SEGREGATION: TOWARDS A
RETROACTIVE SOCIO-SPATIAL SEGREGATION
MODEL
André OUREDNIK : Institut de Géographie de l’Université de Lausanne
andre.ourednick@unil.ch
RESUME. In this project, we build upon Schelling’s spatial segregation model 5 to explore the segregation of households within
a bounded urban area. Our first aim is to eliminate some user-defined initial conditions of the original model, in order to
reach better understanding of socio-spatial segregation dynamics. Our second aim is to explore in which way the spatial
segregation can show retroactive influence on social inequalities.
As modelling environment, we used Northwestern University’s NetLogo 6 , composed of a two-dimensional dynamic simulation
space and of a user-input programming interface. Within this environment, urban space is represented by a 50x50 matrix,
each cell of which can potentially contain one household; households being the model’s agents which eventually segregate.
The basic spatial segregation of households within this model’s space are ruled by Schelling’s model dynamics of movement
induced by intolerance to over-exposition to neighbours of different social class. We have, however, modified the initial
conditions of the original model and added two social segregation dynamics, designed to reach the two aims stated above.
Unlike in Schelling’s model, our social classes are not predefined by variables with fixed values, such as race or sex, but by a
variable with dynamically evolving values representing household wealth. With respect to this variable, the population is
strictly homogenous in our initial conditions. It is only according to our first social segregation dynamic – simulating effects
of wealth division between varying numbers of household descendants – that individual wealth diverges. The newly defined
initial conditions also include an arbitrarily specified class threshold, expressed in terms of divergence from mean wealth; it
is according to this threshold that the population can be divided into two distinct social classes segregating in space. In a
second social segregation dynamic – designed to account for retroaction effects of spatial segregation on social segregation
– we have implemented town-quarter-specific taxes determined by the quarter-population / total-population ratio (as
opposed to taxes determined by the quarter-wealth / total-wealth ratio).
In simulations of this model, we could follow how an originally homogenous population can indeed segregate in space, even
under important variations of the initial conditions of interclass tolerance and class threshold. Thereby, the effect of the
imposition rate seems to be favouring the economic ascension of households which happen to live in quarters with higher
concentrations of already wealthier households. We also observed that, in most cases, the wealthier social class eventually
concentrates in one city quarter, which, due to this concentration, always shows the lowest tax rates. Interestingly, these
socio-spatial segregative effects are reflected in real socio-economic dynamics observable in Switzerland, on national as well
as local scale.
While still under development, the model already yields some intriguing results. Even though conceived as a means of
understanding specific and abstract segregation dynamics, we are confident that its further refinement – such as the
implementation of gentrification dynamics and movement costs – can lead to highly realistic representations of socio-spatial
segregation in today’s urban areas.
Key words: cellular automata – agent-based – segregation – socio-economic – urban geography – tax
5 SCHELLING T. C. [1971] “Dynamic Models of Segregation”, Journal of mathematical sociology, 1, 143-186.
SCHELLING T. C. [1978] Micromotives and Macrobehavior, New York, London: Norton.
6 http://ccl.northwestern.edu/netlogo
7 èmes Rencontres de Théo Quant, janvier 2005