## About

240

Publications

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Introduction

Spatial and complex networks. Statistical physics approach to complex data. Science of cities. Revisiting urban economics and test it with new empirical analysis.

Additional affiliations

January 2009 - present

January 2009 - present

January 2005 - January 2007

## Publications

Publications (240)

Characterizing the spatial organization of urban systems is a challenge which points to the more general problem of describing marked point processes in spatial statistics. We propose a non-parametric method that goes beyond standard tools of point pattern analysis and which is based on a mapping between the points and a ‘dominance tree’, construct...

Most cities in the US and in the world were organized around car traffic. In particular, large structures such as urban freeways or ring roads were built for reducing car traffic congestion. With the evolution of public transportation, working conditions, the future of these structures and the organization of large urban areas is uncertain. Here, w...

The betweenness centrality (BC) is an important quantity for understanding the structure of complex large networks. However, its calculation is in general difficult and known in simple cases only. In particular, the BC has been exactly computed for graphs constructed over a set of N points in the infinite density limit, displaying a universal behav...

Characterizing the spatial organization of urban systems is a challenge which points to the more general problem of describing marked point processes in spatial statistics. We propose a non-parametric method that goes beyond standard tools of point pattern analysis and which is based on a mapping between the points and a "dominance tree", construct...

Floods affected more than 2 billion people worldwide from 1998 to 2017 and their occurrence is expected to increase due to climate warming, population growth and rapid urbanization. Recent approaches for understanding the resilience of transportation networks when facing floods mostly use the framework of percolation but we show here on a realistic...

Floods affected more than 2 billion people worldwide from 1998 to 2017 and their occurrence is expected to increase due to climate warming, population growth and rapid urbanization. Recent approaches for understanding the resilience of transportation networks when facing floods mostly use the framework of percolation but we show here on a realistic...

Simulating nationwide realistic individual movements with a detailed geographical structure can help optimize public health policies. However, existing tools have limited resolution or can only account for a limited number of agents. We introduce Epidemap, a new framework that can capture the daily movement of more than 60 million people in a count...

The betweenness centrality (BC) is an important quantity for understanding the structure of complex large networks. However, its calculation is in general difficult and known in simple cases only. In particular, the BC has been exactly computed for graphs constructed over a set of $N$ points in the infinite density limit, displaying a universal beh...

City planners and urban policy makers require simulation models to understand, predict, design and manage urban areas so that cities can become more sustainable, equitable and efficient. Recently, the idea that one might build 'digital twins' of cities has captured the imagination of many scientists, engineers and policy makers. To unleash the full...

City planners and urban policy makers require simulation models to understand, predict, design and manage urban areas so that cities can become more sustainable, equitable and efficient. Recently, the idea that one might build 'digital twins' of cities has captured the imagination of many scientists, engineers and policy makers. To unleash the full...

Understanding the mechanisms leading to the formation and the propagation of traffic jams in large cities is of crucial importance for urban planning and traffic management. Many studies have already considered the emergence of traffic jams from the point of view of phase transitions, but mostly in simple geometries such as highways for example or...

Understanding the mechanisms leading to the formation and the propagation of traffic jams in large cities is of crucial importance for urban planning and traffic management. Many studies have already considered the emergence of traffic jams from the point of view of phase transitions, but mostly in simple geometries such as highways for example, or...

In most studies, street networks are considered as undirected graphs while one-way streets and their effect on shortest paths are usually ignored. Here, we first study the empirical effect of one-way streets in about 140 cities in the world. Their presence induces a detour that persists over a wide range of distances and is characterized by a nonun...

In most studies, street networks are considered as undirected graphs while one-way streets and their effect on shortest paths are usually ignored. Here, we first study the empirical effect of one-way streets in about $140$ cities in the world. Their presence induces a detour that persists over a wide range of distances and characterized by a non-un...

The science of cities seeks to understand and explain regularities observed in the world’s major urban systems. Modelling the population evolution of cities is at the core of this science and of all urban studies. Quantitatively, the most fundamental problem is to understand the hierarchical organization of city population and the statistical occur...

The science of cities seeks to understand and explain regularities observed in the world's major urban systems. Modelling the population evolution of cities is at the core of this science and of all urban studies. Quantitatively, the most fundamental problem is to understand the hierarchical organization of cities and the statistical occurrence of...

Le développement spectaculaire de l’urbanisation dans le monde s’accompagne d’un grand nombre de problèmes environnementaux et sociaux. Il est devenu essentiel de modéliser les villes, car les décideurs ont besoin de théories solides pour atténuer ces problèmes. Heureusement, la disponibilité croissante de données rend possible la construction d’un...

As mitigating car traffic in cities has become paramount to abate climate change effects, fostering public transport in cities appears ever-more appealing. A key ingredient in that purpose is easy access to mass rapid transit (MRT) systems. So far, we have however few empirical estimates of the coverage of MRT in urban areas, computed as the share...

As mitigating car traffic in cities has become paramount to abate climate change effects, fostering public transport in cities appears ever-more appealing. A key ingredient in that purpose is easy access to mass rapid transit (MRT) systems. So far, we have however few empirical estimates of the coverage of MRT in urban areas, computed as the share...

The airline industry was severely hit by the COVID-19 crisis with an average demand decrease of about $64\%$ (IATA, April 2020) which triggered already several bankruptcies of airline companies all over the world. While the robustness of the world airline network (WAN) was mostly studied as an homogeneous network, we introduce a new tool for analyz...

The coupling between population growth and transport accessibility has been an elusive problem for more than 60 years now. Due to the lack of theoretical foundations, most of the studies that considered how the evolution of transportation networks impacts the population growth are based on regression analysis in order to identify relevant variables...

Understanding how interurban movements can modify the spatial distribution of the population is important for transport planning but is also a fundamental ingredient for epidemic modeling. We focus here on vacation trips (for all transportation modes) during the Chinese Lunar New Year and compare the results for 2019 with the ones for 2020 where tr...

Urban science seeks to understand the fundamental processes that drive, shape and sustain cities and urbanization. It is a multi/transdisciplinary approach involving concepts, methods and research from the social, natural, engineering and computational sciences, along with the humanities. This report is intended to convey the current “state of the...

The recent availability of data about cities and urban systems opens the exciting possibility of a ‘new Science of Cities’. Urban morphogenesis, activity and residence location choice, mobility, urban sprawl and the evolution of urban networks are just a few of the important processes that can be discussed now from a quantitative point of view. Her...

Scaling describes how a given quantity Y that characterizes a system varies with its size P. For most complex systems, it is of the form
Y
∼
P
β
with a non-trivial value of the exponent β, usually determined by regression methods. The presence of noise can make it difficult to conclude about the existence of a nonlinear behaviour with β ≠ 1 and...

The coupling between population growth and transport accessibility has been an elusive problem for more than 60 years now. Due to the lack of theoretical foundations, most of the studies that considered how the evolution of transportation networks impacts the population growth are based on regression analysis in order to identify relevant variables...

In the classic model of first-passage percolation, for pairs of vertices separated by a Euclidean distance L, geodesics exhibit deviations from their mean length L that are of order Lχ, while the transversal fluctuations, known as wandering, grow as Lξ. We find that when weighting edges directly with their Euclidean span in various spatial network...

Scaling describes how a given quantity $Y$ that characterizes a system varies with its size $P$. For most complex systems it is of the form $Y\sim P^\beta$ with a nontrivial value of the exponent $\beta$, usually determined by regression methods. The presence of noise can make it difficult to conclude about the existence of a non-linear behavior wi...

Car traffic in urban systems has been studied intensely in past decades but models are either limited to a specific aspect of traffic or applied to a specific region. Despite the importance and urgency of the problem we have a poor theoretical understanding of the parameters controlling urban car use and congestion. Here, we combine economical and...

Cities are systems with a large number of constituents and agents interacting with each other and can be considered as emblematic of complex systems. Modeling these systems is a real challenge and triggered the interest of many disciplines such as quantitative geography, spatial economics, geomatics and urbanism, and more recently physics. (Statist...

In the classic model of first passage percolation, for pairs of vertices separated by a Euclidean distance $L$, geodesics exhibit deviations from their mean length $L$ that are of order $L^\chi$, while the transversal fluctuations, known as wandering, grow as $L^\xi$. We find that when weighting edges directly with their Euclidean span in various s...

Cities are systems with a large number of constituents and agents interacting with each other and can be considered as emblematic of complex systems. Modeling these systems is a real challenge and triggered the interest of many disciplines such as quantitative geography, spatial economics, geomatics and urbanism, and more recently physics. (Statist...

Motivated by the shape of transportation networks such as subways, we consider a distribution of points in the plane and ask for the network G of given length L that is optimal in a certain sense. In the general model, the optimality criterion is to minimize the average (over pairs of points chosen independently from the distribution) time to trave...

Challenges due to the rapid urbanization of the world — especially in emerging countries — range from an increasing dependence on energy to air pollution, socio-spatial inequalities and environmental and sustainability issues. Modelling the structure and evolution of cities is therefore critical because policy makers need robust theories and new pa...

Characterizing the spatio-temporal evolution of networks is a central topic in many disciplines. While network expansion has been studied thoroughly, less is known about how empirical networks behave when shrinking. For transportation networks, this is especially relevant on account of their connection with the socio-economical substrate, and we fo...

Motivated by the shape of transportation networks such as subways, we consider a distribution of points in the plane and ask for the network $G$ of given length $L$ that is optimal in a certain sense. In the general model, the optimality criterion is to minimize the average (over pairs of points chosen independently from the distribution) time to t...

Characterizing the spatio-temporal evolution of networks is a central topic in many disciplines. While network expansion has been studied thoroughly, less is known about how empirical networks behave when shrinking. For transportation networks, this is especially relevant on account of their connection with the socio-economical substrate, and we fo...

Car traffic in urban systems has been studied intensely in past decades but its analysis is often limited to empirical observations and agent-based modelling, and despite the importance and urgency of the problem we have a poor theoretical understanding of the parameters controlling urban car use and congestion. Here, we combine economical and tran...

Planar graphs and their spatial embedding—planar maps—are used in many different fields due to their ubiquity in the real world (leaf veins in biology, street patterns in urban studies, etc.) and they are also fundamental objects in mathematics and combinatorics. These graphs have been well described in the literature, but we do not have so far a c...

Networks embedded in space can display all sorts of transitions when their structure is modified. The nature of these transitions (and in some cases crossovers) can differ from the usual appearance of a giant component as observed for the Erdos-Renyi graph, and spatial networks display a large variety of behaviors. We will discuss here some (mostly...

Networks embedded in space can display all sorts of transitions when their structure is modified. The nature of these transitions (and in some cases crossovers) can differ from the usual appearance of a giant component as observed for the Erdös–Rényi graph, and spatial networks display a large variety of behaviors. We will discuss here some (mostly...

Planar graphs and their spatial embedding -- planar maps -- are used in many different fields due to their ubiquity in the real world (leaf veins in biology, street patterns in urban studies, etc.) and are also fundamental objects in mathematics and combinatorics. These graphs have been well described in the literature, but we do not have so far a...

The betweenness centrality, a path-based global measure of flow, is a static predictor of congestion and load on networks. Here we demonstrate that its statistical distribution is invariant for planar networks, that are used to model many infrastructural and biological systems. Empirical analysis of street networks from 97 cities worldwide, along w...

Although the average population density of a city is an extremely simple indicator, it is often used as a determinant factor for describing various aspects of urban phenomena. On the other hand, a plethora of different measures that aim at characterizing the urban form have been introduced in the literature, often with the risk of redundancy. Here,...

Another way to think of planar networks is by focusing on their faces and how to generate them. An example is given by tessellations of a plane that are divisions of the plane into polygons. There is a vast literature on tessellations (see [188] and references therein) and in this chapter, we will discuss selected examples only. Many tessellations...

There are many centralities that characterize the importance of a node (or an edge) in a large network. Among all these centralities, the betweenness centrality (BC) captures important aspects of the network and its structure. For complex networks, the BC generally scales with the degree, showing that in general central nodes are the hubs. In spati...

Despite a large number of studies on planar networks, there is still a lack of global, high-level metrics allowing to characterize their structure and geometrical patterns.

Variational approaches have been largely disregarded in complex network studies although they frequently provide an alternative and possibly more meaningful point of view. This important class of network models is obtained by looking for graphs that optimize a given quantity, functional of the graph. The simplest case is, for example, the minimum s...

Nodes in networks are in general defined by their connectivity properties but could also carry another type of information. In the case where nodes represent cities, the population is a natural attribute that can be attached to each node. In the case of spatial networks with attributes on nodes, we can foresee the problem of correlating their topol...

As we saw throughout this book, despite the many studies in graph theory and combinatorics, neurophysiology, botanic, geography, and transport studies among others, we do not have a full understanding of the structure and evolution of spatial networks. In addition, these networks are not just simple structures embedded in a substrate but constitute...

From a theoretical point of view, an important problem amounts to understand the structure of random planar graphs and eventually to propose a classification of these objects. In this chapter, we will discuss three different approaches. In the first one, we discuss the statistics of the area and shape of faces, and we apply this to street networks....

The most important model of a random graph where nodes are connected at random was proposed by Erdos and Renyi [242] and constitutes an archetype—or at least a benchmark—for constructing more complex random graphs. It is then natural to ask if we can extend this model to the case where nodes are located in space. In this chapter, we will discuss so...

In this chapter, we discuss the random geometric graph (also called the unit disk graph) which is an important model for spatial networks. We will also introduce and discuss some of the variants of this model. The random geometric graph is obtained from a random distribution of points in the plane and a geometric rule for connecting these points an...

A problem that can be faced when studying networks is the abundance of measures. This is particularly true for spatial networks where the combination of spatial and topological metrics contributes to the explosion of possible measures, and it is obviously worse when these networks evolve in time. In order to select the most relevant tools for chara...

Most networks, including spatial graphs, evolve and grow in time. Understanding the main processes governing this growth and the resulting structure is, therefore, crucial in many disciplines ranging from urban planning to the study of neural networks.

We discussed in the previous Chaps. (1–6) how to characterize the structure of spatial networks. In many instances, however, these networks are evolving in time, growing, and expanding in space. This is typically the case of transportation networks such as roads, subways, and railways, but also for biological networks. It is therefore important to...

The study of spatial networks – networks embedded in space – started essentially with quantitative geographers in the 60–70 s who studied the structure and the evolution of transportation systems. The interest for networks was revived by Watts and Strogatz who opened the way to a statistical physics type of analysis and modeling of large networks....

In Chap. 12, we discussed models of networks defined by the optimization of a single quantity that depends on the global structure of the network. In contrast, we consider here the growth of networks where nodes are added one by one, located at random and connected to the network in an optimal way.

Many studies on complex networks were about how to characterize them and what are the most relevant measures for understanding their structure. In particular, the degree distribution and the existence of the second moment for an infinite network were shown to be critical when studying dynamical processes on networks. These behaviors are therefore s...

Les effets de la densité sur les coûts des infrastructures et services publics

This book develops a morphodynamical approach of spatial networks with a particular emphasis on infrastructure networks such as streets, roads and transportation networks (subway, train). The author presents the mathematical tools needed to characterize these structures and how they evolve in time. The book discusses the most important empirical re...

Scaling has been proposed as a powerful tool to analyze the properties of complex systems, and in particular for cities where it describes how various properties change with population. The empirical study of scaling on a wide range of urban datasets displays apparent nonlinear behaviors whose statistical validity and meaning were recently the focu...

Recent years have witnessed an explosion of extensive geolocated datasets related to human movement, enabling scientists to quantitatively study individual and collective mobility patterns, and to generate models that can capture and reproduce the spatiotemporal structures and regularities in human trajectories. The study of human mobility is espec...

We analyze the coalescing model where a `primary' colony grows and randomly emits secondary colonies that spread and eventually coalesce with it. This model describes population proliferation in theoretical ecology, tumor growth and is also of great interest for modeling the development of cities. Assuming the primary colony to be always spherical...

We study structural properties of street networks from 97 of the most populous cities worldwide at scales significantly larger than previous studies. We find that the distribution of betweenness centrality (BC), a global structural metric based on network flow, is invariant in all studied street networks, despite the obvious structural differences...

We analyze a dataset providing the complete information on the effective plays of thousands of music listeners during several months. Our analysis confirms a number of properties previously highlighted by research based on interviews and questionnaires, but also uncover new statistical patterns, both at the individual and collective levels. In part...

Random planar graphs appear in a variety of contexts and it is important for many different applications to be able to characterize their structure. Local quantities fail to give interesting information and it seems that path-related measures are able to convey relevant information about the organization of these structures. In particular, nodes wi...

In empirical studies of random walks, continuous trajectories of animals or individuals are usually sampled over a finite number of points in space and time. It is however unclear how this partial observation affects the measured statistical properties of the walk, and we use here analytical and numerical methods of statistical physics to study the...