## 1 Introduction  
Urban centers are becoming increasingly attractive for people in developing and developed countries and the transitions of people toward the cities has rapidly grown in the past 40 years. In 1950, in general about 2/3 of the world population lived in rural settlements and 1/3 was living in urban areas to exploit working conditions and opportunities. The share of the global population living in urban areas has increased from one third in 1960 to 55% (4.1 billion people) in 2018 [1]. The world's urban population is now increasing by 60 million persons per year, about three times the increase registered in the rural population [2]. Growing urbanization is a consequence of the new births in urban zones and of continued migration of people coming from the rural surroundings. These movements are also enhancing the sprawl of urban spaces as before rural peri-urban settlements were combined into nearby cities and secondary cities, connected by commerce activities developed in larger urban centers [3]. The process of urbanization is expected to strongly endure in the next century. By 2030, it is projected that nearly 5 billion of the world's 8.1 billion people will live in urban developments, which means 61% of the population. The less-developed regions will be more than 57% urban. Latin America and the Caribbean will actually have a greater percentage of inhabitants living in cities than in Europe [4] because of the disparity of conditions and services that people can find in the city centers. In the past, the movement from rural areas to the cities could guarantee better living conditions, however there is scientific evidence that now this assumption is not always valid. There is a high disparity in living conditions between downtown and the surroundings in US [5], European and Asian cities [6]. Worldwide, the number of metropolises with 10 million or more inhabitants is increasing rapidly, configuring new'megacities' located in the less-developed areas of the world. In 1960, only New York and Tokyo had more than 10 million people, by 1999 the number of cities with more than 10 million people around the world was 17, with 13 located in developing regions [7]. Currently, urban centers occupy less than 5% of the world's mainland, using over two-thirds of the total energy, and they are responsible for over 70% of CO\({}_{2}\) emissions, according to the C40 Cities Climate Leadership Group [8]. In 2050, the outlook is that 6 billion people will live in urban zones, worldwide. Thus, innovation in urban infrastructure and technology is essential when addressing sustainable and low-impact solutions to support anthropic activities and urban growth and to reduce the cities' impact. As an example, by 2030, greenhouse gas (GHG) emissions could be reduced by up to 1.5 billion metric tons CO\({}_{\text{2 eq}}\) annually, mainly through a massive transformative change in the transport systems in the world's 724 largest cities [9]. The availability of a pervasive communication infrastructure, wireless [10] or cable [11], in the city of the future is a prerequisite to enable services and solutions to improve sustainability in the use of the energy resources [12; 13]. How to manage this incomparable urban expansion in following years is likely to decide the outcome of the sustainability endeavors that are spreading through different sectors [14]. The global trends of urbanization in the first decades of the 21 st century are meaningfully transformed from the preceding experiences in terms of urban change. For instance, urbanization is taking place at lower levels of economic development and the majority of future urban population increase will take place in developing countries where the aggregation of people in the urban centers often occurs in informal settlements [15].