  We discuss the applicability of classical control theory to problems in smart
grids and smart cities. We use tools from iterated function systems to identify
controllers with desirable properties. In particular, controllers are
identified that can be used to design not only stable closed-loop systems, but
also to regulate large-scale populations of agents in a predictable manner. We
also illustrate by means of an example and associated theory that many
classical controllers are not be suitable for deployment in these applications.
