Abstract
The shape of urban settlements plays a fundamental role in their sustainable planning. Properly defining the boundaries of cities is challenging and remains an open problem in the science of cities. Here, we propose a worldwide model to define urban settlements beyond their administrative boundaries through a bottom-up approach that takes into account geographical biases intrinsically associated with most societies around the world, and reflected in their different regional growing dynamics. The generality of the model allows one to study the scaling laws of cities at all geographical levels: countries, continents and the entire world. Our definition of cities is robust and holds to one of the most famous results in social sciences: Zipf’s law. According to our results, the largest cities in the world are not in line with what was recently reported by the United Nations. For example, we find that the largest city in the world is an agglomeration of several small settlements close to each other, connecting three large settlements: Alexandria, Cairo and Luxor. Our definition of cities opens the doors to the study of the economy of cities in a systematic way independently of arbitrary definitions that employ administrative boundaries.
Highlights
What are cities? In The Death and Life of the Great American Cities, Jacobs argues that human relations can be seen as a proxy for places within cities [1]
We propose a worldwide model based on the city clustering algorithm (CCA), called the city local clustering algorithm (CLCA), to define cities beyond their usual administrative boundaries, and to take into account the intrinsic cultural, political and geographical biases associated with most societies and reflected in growth without merging (b) tth reference cluster sth reference cluster rth reference cluster forbidden growth by the region largest D*
We justify our choices with the following assumptions: (i) D(min) = 100 people km−2, a value slightly greater than the lower bound CCA parameter (D∗ = 50 people km−2) used to define the regions of clusters; (ii) D(max) = 1000 people km−2, a loosened value of D(max) = ∞; (iii) δ = 10 people km−2, a small enough value to avoid the reference clusters growing without merging; (iv)
Summary
What are cities? In The Death and Life of the Great American Cities, Jacobs argues that human relations can be seen as a proxy for places within cities [1]. We propose a worldwide model to define urban settlements beyond their usual administrative boundaries through a bottom-up approach that takes into account cultural, political and geographical biases naturally embedded in the population distribution of continental areas. Our conjecture is straightforward: there are hierarchical mechanisms, similar to those present in previous studies of cities in the UK [14] and brain networks [46], behind the growth and innovation of urban settlements These mechanisms are ruled by a combination of general measures, such as the population and the area of each city, and intrinsic factors which are specific to each region, e.g. topographical heterogeneity, political and economic issues, and cultural customs and traditions. If political turmoil or economic recession plagues a metropolis for a long time, all of its satellites are affected too, i.e. the entire region ruled by the metropolis will be negatively impacted
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