From human mobility to urban service networks: a distance-based model for systemic risk assessment

The construction of a network for assigning users to essential socio-economic services at the urban level provides a powerful framework to represent the web of functional connections that are exposed to natural hazards. Such a representation is particularly relevant for natural risk assessments, as it enables the analysis not only of direct damages to assets and services, but also of indirect and cascading impacts arising from service disruptions and user reallocation processes (e.g. during flood events). Building this type of network requires an understanding of decision-making factors, both individual and non-individual, which depend on multiple parameters, from economic to social. Despite this complexity, it is possible to reduce the modelling of these mechanisms to the analysis of a limited set of behavioural variables, such as the distance between the service and the user’s residence.

Based on millions of human movements, we highlight how to generate realistic flows of home–essential service users on an urban scale according to a distance-based universal law of service attractiveness. To do this, we incorporate the city road network into the distribution of populated buildings using demographic data, assigning an attractiveness value to the path to the service among all possible choices.

By showing how the universal law of service attractiveness depends on the size of the city, our study demonstrates that the larger the city under analysis, the more rapidly the attractiveness distribution of the service declines, and vice versa. Moreover, we highlight how service attractiveness is influenced by the type of essential service selected, distinguishing those for which people are most willing to travel long distances in order to benefit from them.

Our model, in addition to enabling the generation of a socio-economic network of assigned users to essential services—useful for various areas of research such as epidemiology and urban risk—bridges the gap between distance- and opportunity-based models of human mobility, characterising users’ decision-making mechanisms across multiple spatial scales and for different types of essential services through a distance-based universal law of service attractiveness.