Never has geography been so present in our societies. For centuries, stimulated by the curiosity of travelers, the appetite of merchants, and the greed of powers, knowledge about the planet, its resources, and the riches of its cities and territories has never ceased to increase while remaining the privilege of the powerful. Precise knowledge of the terrain was an essential prerequisite for the great strategist Sun Tzu, in his famous book, The Art of War, published in China’s warring kingdoms during the Spring and Fall period in the 5th Century BCE. The French geographer Yves Lacoste confirmed, as recently as 1976, the strategic capacities of the discipline by showing in his provocatively-named book, La géographie, ça sert, d’abord, à faire la guerre (Geography primarily serves to make war), that it was supported in France by a nationalist and imperialist state power.

In France, geographic learning has been a requirement for all students in school curricula since 1870. However, it is especially since the emergence of mobile phones in the early 2000s that geography has been a factor in daily life. Even in the poorest countries, a very large majority of people are able to connect to the Internet, see images and maps from around the world, use satellite positioning services, GPS, Galileo, Glonass, or Baidu, to mark routes, navigate the world, geolocate, or make themselves visible to nearby “services” and “friends”. This revolution surpasses, by the number of applications it generates and the extent to which they are shared, the one that has occurred more discreetly since the 1970s with the widespread use of geographical information systems (GIS), in administrations, for spatial planning, and in companies, for logistics management. The limited capacity of the computers of the time and the insufficient competence of the services in the analysis and modeling of spatial data have long slowed down the effective integration of these tools into many activities (Goodchild 2016).

One of the current challenges in fully exploiting the new major computer capacities and democratizing geographical information is to make judicious and appropriate use of the knowledge and skills accumulated about cities and territories, not only through geography, but also by all disciplines that have sooner or later integrated the “spatial turn” into their research approaches, from agronomy to archeology and from history to epidemiology.

These disciplines share the construction of models, which are above all summaries of knowledge, simplified in relation to the diversity and complexity of individual cases, but communicable and improvable because they are codified, at a given moment in the state of knowledge, by mathematical or computer formalizations. The knowledge integrated into a model represents sets of recurrent facts in empirical observations, which have been selected according to the hierarchy of their effects on the problem being studied, with more or less parsimony depending on whether we focus on the generality or precision of the results. Calculation or simulation is used to propose predictions, or to explore possible scenarios, as part of the model assumptions. According to appropriate granularities and levels of resolution, all forms of modeling can be used with extremely variable objectives: laboratory hypothesis tests for theoretical models, serious games with a didactic function, support models designed to solve difficult situations including contradictory or even conflicting issues, models inserted in interactive applications intended for information or decision support, commonplace models generally used for location choices or infrastructure templates, and so on.

Critics of models often denounce oversimplification, or selection bias, and question the quality of the data used to validate them. Admittedly, each model has its shortcomings and deficiencies, but the great advantage of modeling, compared to the subtleties of written or spoken rhetoric, is that it requires very detailed clarification of the assumptions of discourse and intentions in order to better share them. Modelers are informed of the defects and deficiencies of their models; they are the first to deplore them and are constantly trying to overcome them.

The uses and functions of the models are multiple. They are often designed for prediction (meteorological and financial models), more broadly data mining models, for the validation of an analytical theory (economic models) or, in geography, for the planning and discussion of territorial issues (decision support models and companion models), but social science modeling develops practices that are much broader and richer than those anchored in the traditional scientific imagination. Models are also used to deepen and test explanations using an abductive approach (Besse 2000) that interacts with conceptual constructions and empirical data, as will be shown in several chapters of this book.

Several publications have already proposed more or less ambitious syntheses of geographic modeling. For this expression in French, the Google Scholar algorithm offers some 40,000 references, which are mainly journal articles. Collective books or textbooks are less common. The book published by Lena Sanders in 2001 is pioneering in this field. The work of Yves Guermond (2005) compiles the productions and practices of the laboratory of the University of Rouen. Others have focused on the important processes of spatiotemporal change (Mathian and Sanders 2014) or only deal with certain urban models (Antoni et al. 2011; Bonhomme et al. 2017). Most recently, two books by Arnaud Banos (2013, 2016) and one by Frank Varenne (2017) laid the foundations for epistemological and philosophical reflection on geographical models.

The book we propose here is part of a multidisciplinary collection. It is designed to provide didactic information on the modeling process, in its particularities justified by the handling of geographical concepts and information, and illustrated with examples representative of the major innovations that have taken place over the past decade. Chapter 1 recalls the foundations of the geographical discipline on which models can be based to take into account the complexity in the organization and evolution of cities and territories. Chapter 2 deciphers the crucial choices for modeling, which are at the root of the diversity of models and their uses: we examine to what extent the complex can be simplified or, on the contrary, how can we try to integrate it into the models. Chapter 3 describes the models that establish explicit relationships between contrasting spatial morphologies, which present inequalities on different scales, and the social processes that generate them, according to “micro–macro” dynamics. Chapter 4 explores the construction stage of city and territory models and proposes a new incremental multi-modeling method. Chapter 5 introduces various possible uses of a simulation platform, OpenMOLE, which uses evolutionary algorithms and provides access to HPC equipment. Finally, Chapter 6 is devoted to the new visualization tools that are so important for model exploration and validation, as well as for communicating their results.

At the end of the book, the index brings together the main concepts that characterize geographical modeling. For the concepts that are already precisely defined in the chapters devoted to them, the multiple page numbers that testify to their appearance throughout the book make it possible to understand how they also apply to widely shared intellectual and practitioner approaches. Moreover, essential concepts such as “space”, “simulation”, “territory”, “city”, and “visualization” do not appear in the index because they are used and enriched many times by all of the authors. It is also because of the great coherence of these texts that the bibliographical references, which often appear several times, are grouped into one list at the end. This provides an original and updated state of the art on the major parallel and convergent directions in geographical modeling.

Introduction written by Denise PUMAIN.