Since 2007, more than half of the world’s population has been living in urban areas and the figure is estimated to exceed 70 per cent by 2050. This is a hallmark of the transformation of humans’ economic base and social structure, inasmuch as, previously, populations lived and worked primarily in rural areas. By concentrating people, investment and resources (a process known as agglomeration), cities heighten the possibilities for economic development, innovation and social interaction. More specifically, cities also make it possible to lower unit costs so as to provide public services such as water and sanitation, health care, education, electricity, emergency services and public recreational areas (Polese, 2009, Satterthwaite, 2010). Along these lines, cities also face challenges that threaten their efforts to achieve sustainability, for example, through improvement of access to, and efficiency in the use of, public services, as well as reduction of their ecological footprint and financial fragility, and the building of resilience against the adverse impact of natural hazards.