More than half the world's population lives in cities. This has led to a rapid process of urbanization of different areas in order to have enough space to accommodate this large number of people. In this context, understanding the interaction between the urban organisation and key characteristics such as the infrastructure network, population distribution, sustainability or public services becomes crucial.
Traditionally, indicators of urban organisation such as population density, land use or infrastructure distribution were obtained from expensive surveys and satellite images. However, mobile technologies make it possible to obtain much more accurate, instantaneous and in greater numbers human mobility data.
A study carried out with the participation of IFISC researchers and published in the journal Nature Communications has analysed the hierarchical organisation of human mobility and how this relates to transport, pollution and health in cities. In order to carry out the study, the journeys of more than 300 million people have been analysed. This anonymized and aggregated data was obtained through Google's User Location History and includes the journeys of residents and visitors from different cities around the world. The data includes 174 of the world's most populous cities, as well as 127 North American cities (those with more than 400,000 inhabitants).
To study the hierarchical structure of cities, the regions of each city have been classified into levels of activity (or "Hotspots") according to the number of trips concentrated in them. Thus, cities with similar population levels show different spatial distributions of these levels of activity, being able to be concentrated in concentric rings like the layers of an onion (the case of Paris), spread in one direction (Bangkok) or mixed throughout the city (Sydney).
Once assigned a level of activity to each region, researchers have formulated a metric to quantify how hierarchical is the mobility between these regions of cities. In short, this metric captures the extent to which flows are concentrated between centres with a similar level of activity. The results of the article show that cities have a rich variety at the organizational level. Not only that, the hierarchical organisation of mobility appears to be correlated with indicators such as the use of public transport, pollution, the health of citizens or the integration of different communities of inhabitants, with cities with a higher hierarchical flow (i.e. more journeys between hotspots with similar levels of activity) tending to show more positive values for these indicators.
This study analyzes the importance of urban organization, being those that guarantee a better connection between similar socioeconomic centers the ones that present more positive values in the analyzed indicators. As it is based solely on mobility, the metrics developed in this study are easily updatable, as well as being deployed in the less favoured regions of the planet at a very reduced cost.
Aleix Bassolas, Hugo Barbosa-Filho, Brian Dickinson, Xerxes Dotiwalla, Paul Eastham, Riccardo Gallotti, Gourab Ghoshal, Bryant Gipson, Surendra A. Hazarie, Henry Kautz, Onur Kucuktunc, Allison Lieber, Adam Sadilek, and José J. Ramasco. Hierarchical organization of urban mobility and its connection with transportation, pollution and health. Nature Communications. DOI: https://doi.org/10.1038/s41467-019-12809-y