Observing cities as a complex system

Cities are some of the most intricate and advanced creations of humanity. Most objects in cities are perfectly synchronised to coordinate activities such as jobs, education, transportation, entertainment, and waste management. Although each city has its own characteristics, some commonalities can be observed across most cities, such as issues related to noise, pollution, segregation, and others. Further, some of these issues might be accentuated in larger or smaller cities. For example, with more people, a city might experience more competition for space, so rents would be higher. The urban scaling theory provides a framework for analysing cities in terms of their size. New data for analysing urban scaling theory allow for an understanding of how urban metrics change with population size, whether they apply across most regions, or whether patterns correspond only to some countries or regions. Yet, reducing a city and all its complexity to a single indicator might simplify urban areas to the extent that their disparities and variations are overlooked. Often, the differences in living conditions across different parts of the same city are greater than the degree of variation observed between cities. For example, in terms of rent or crime, within-city variations might be more significant than between cities. Here, we review some urban scaling principles and explore ways to analyse variations within the same city.