Figure 1.2 - Map of subareas related to the smart city concept Source: Winkowska et al. (2019). Main challenges: the key dimensions that a sustainable city must address Modern cities face challenges along various dimensions. We identify and examine nine of these below. A- Uncontrolled urban sprawl For some scholars, the way in which human beings “develop . air pollution; increased physical infrastructure costs; income . . urban areas is a critical component to creating livable and inequality; and social heterogeneity (in the form of either sustainable cities. The footprint of major metropolitan areas, gentrification or slums). Later on, urban consumption, social suburbs, and small towns ultimately shapes the environmental inclusiveness, green areas, the planting and maintaining of and social conditions within our communities.”42 urban trees, and the health of citizens became major topics for city executives, city planners, and citizens. Among different types of development pattern, “sprawl” has been the subject of heightened scrutiny from urban planners Urban planners and scholars are now working on different and policy makers. Sprawl constitutes unmanaged geographical urban and suburban development patterns, frequently expansion of a city through the construction, in accordance with proposing urban transformation as an alternative to expansion. the availability and cost of land, of low-density areas (individual Since many cities around the world were not built according housing) whose residents depend on cars to access work and to some form of master plan, understanding the motivations, amenities. Where a city has developed through sprawl, the consequences, and policy implications of previous development border between urban and rural areas is usually poorly defined. patterns can yield important insights about how to build up more For many years, only a few people and organizations raised sustainable communities over the long term. Many analysts concerns about the negative impact of this sprawling type of agree that there is a need for sustainable urban planning and urban development: housing fragmentation; soil, water, and for sensible choices to be made between densification and (42) Brody S. (2013). The Characteristics, Causes, and Consequences of Sprawling Development Patterns in the United States. Nature Education Knowledge 4(5):2 https://www.nature.com/scitable/knowledelibrary/the-characteristics-causes-and-consequences-of-sprawling-103014747/g/ 41 Quélin and Smadja | HEC PARIS | SMART CITIES | The sustainable program of six leading cities | 2021