# IoT-Enabled Smart Sustainable Cities: Challenges and Approaches
## 5 Future Research Directions  
The objectives detailed in Section 2 and the indicators discussed in Section 3 (on the basis of which a smart city may evolve) can be taken as guidelines by cities worldwide in order to scale up and improve their value for the different actors interacting with them [138]. As highlighted also in Section 4, this is even supported by a strong communication and rational decision making, together with the promotion of private-public partnership projects, and efficient and focused synergies between old cities and new cities, along with differentiated city models, as proposed for the Korean city of Gyeonggi-do [139]. With regard to these city models, the following city categories, valid for cities all over the world, can be defined; (i) efficient city management, (ii) regional regeneration, (iii) low-carbon eco-friendly, and (iv) industry development-oriented [140]. Concerning the _efficient city management_ category, London and Glasgow, England, plan to introduce a smart system to provide citizens with better city infrastructures for environment and job [141, 142], thus expanding city services required by businesses. The final aim is to increase the efficiency of urban management, in order to foster technology innovation industry, and to secure the quality of life. In a similar way, the Smart America project [143] in the US has been implemented with the goal of applying Cyber-Physical Systems (CPSs) to the real world, in order to enable different technologies (e.g., home/building, climate/environment, disaster recovery, manufacturing, transportation, healthcare, security, and energy) in several daily contexts. The _regional regeneration_ category is representative of the innovation processes implemented in the European cities of Copenhagen, Denmark, and Barcelona, Spain. In detail, the Copenhagenmunicipality is promoting the cooperation between the government itself and the citizenship [144], aiming at developing an ecosystem in which private, business, public, and citizens cooperate and perform innovation activities in a given space or area (e.g., regarding the Danish port slum problem). Instead, the government of Barcelona is providing heterogeneous city-related data to citizens and public services [145], in order to easily access information, eco-friendly transportation infrastructure, and improve the residential environment of the urban space, thereby regenerating the urban space in an economical manner (e.g., regarding the municipal bike sharing service [146, 147]). With regard to the _low-carbon eco-friendly_ category, different smart city-oriented projects will be applied in other two EU cities (namely, Nice, France, and Amsterdam, the Netherlands) and in Singapore [148]. The French city is designing an _eco-city_ zone in the city center [149], in order to establish a municipal plan suitable to maintain environmentally-friendly cultural city, collecting various city data and providing the output of their consequent processing to citizens, aiming at improving citizen's convenience quality of life [150]. In a similar way, the Dutch city of Amsterdam, by combining technology and social infrastructures, is building a sustainable economic growth and safe society, thus aiming at reducing the annual amount of CO2 by using electric vehicles, smart building, smart grids, and smart meters [151, 152]. Finally, the _industry development-oriented_ category is illustrative of the initiatives taking place in Dubai, UAE, and in different cities in Japan. Dubai is planning to develop smart cities that can easily and quickly deliver information--including public services, education, health and security--through smart devices, to their citizens and tourists [153], while Japan has a long-term smart city development plan facilitating information collection [154, 155, 156].