Urban

It is an established fact that urbanization in developed countries is accompanied by economic growth and industrialization with a mutually self-reinforced mechanism [1]. This historic pattern generated the expectation of a virtuous circle between economic growth and urbanization regardless local conditions. From classic urban economic theories to the more recent scaling approach to cities [2], the growth of urban population was routinely used as a proxy of economic growth. There are several theories aimed to explain urbanization processes.

The accurate estimation of human activity in cities is one of the first steps towards understanding the structure of the urban environment. Human activities are highly granular and dynamic in both the spatial and temporal dimensions and having a clear idea about the whereabouts of these activities is crucial for decision-making in numerous applications, such as urban management, retail, transport planning and emergency management.

Zipf's law and urban scaling are two fundamental paradigms researched in urban science. They have mostly been investigated independently and are perceived as disassociated matters. Here we present a large scale investigation about the connection between these two laws using population and GDP data from 96 countries. We empirically demonstrate that both laws are tied to each other and derive an expression relating the exponents.

Empirical evidence has been shown that some urban variables scale non-linearly with the city population size.
More specifically, some socio-economic variables, such as the number of patents, wages and GDP, show a super-linear behaviour with the population of the city. On the other hand, infrastructure variables, such as the number of gas stations and length of streets, scale sub-linearly with the city population, generating a scale economy.