Cities are systems of systems of systems. These are often viewed through their subsystems, e.g. transportation, retail, health, welfare, crime, finance, water, political, refuse disposal, and so on. Any of these subsystems has its own subsystems, without clear boundaries, but they impact on and are impacted on by other subsystems. Some things are at discernable micro-, meso- and macro-levels, with surprising interactions between those levels. They have multilevel dynamics, and new self-organised subsystems can emerge while existing subsystems can disappear, e.g. ghettos can emerge, bus routes can disappear. There can be problems from unexpected interactions between systems through overlooked connectivities, and problems can occur due to a...