Scholars, from scientists to artists, have been drawing analogies between the human body and the built environment for centuries. The functioning of major transportation networks within a city has frequently been explained in terms of how the circulatory system in a body works, and vice-versa, with major roadways compared with arteries and veins. The comparisons are surprisingly interesting. In both systems, major and minor pathways exist, with varying capacities and roles that connect and/or service different functional components of the overall city or of the body. In both systems, clogging, with its unfortunate consequences is caused by either temporary blockage or longer-term capacity reduction due to narrowing of pathways. A blockage at one point can affect far-removed locations. Mathematical models that bear some similarities have been developed to describe each of these systems. In the urban context, for example, the effects of closing a major pathway on traffic redistribution throughout the whole system of roadways can be predicted. These models find everyday use in our cities.

Although analogies between urban functions and human bodily functions are common, we should carefully think about their appropriate use. The two systems are obviously radically different for innumerable reasons, and this in turn undermines the usefulness of the analogy. It is axiomatic that nothing can ever be proven by use of analogies or metaphors to begin with. Analogies or metaphors, however, do often prompt the scholars or researchers in each field to view their own problems in a different light. New approaches to thorny issues are occasionally suggested (4).