ABSTRACT
This essay introduces the idea that cities evolve from the bottom up, that patterns emerge
as a global order from local decisions. As the future is unknowable, cities must be planned
according to this type of complexity. We begin by introducing the idea of hierarchy and
modularity as the basis of a generative process that leads to patterns that are self-
similar over many scales, patterns that are fractal in their structure. We then present
a simple model of growth that generates such patterns based on a trade-off between
connecting to the growing structure and seeking as much free space as possible around
any location within it. These are the tensions that exist in real cities through the quest
by individuals to agglomerate. Once we have sketched the model, we demonstrate
how this generative process can be simulated using cellular automata, allowing us to
think of the logic in terms of rules that represent how existing development takes place.
