Open data are gold mines because they can be used to create services that develop a smart city while improving users' living conditions. Several research works go in this direction, presenting open data impact in the smart city for some, while others have focused on data processing methods. We have therefore deemed it necessary to make a state of the art on these different issues. The particularity of our study is that it shows the link between open data and smart city in all its aspects, describing what kind of open data is suitable for the smart city, how it is important for its development, and how these open data are processed to create services. Thus, in this article, we first present a review of existing surveys since 2015. Then, we present different smart city dimensions based on open data as well as some applications, and we detail how to process these data. We end with a list of open data sources as well as some challenges and solutions related to smart city services.
INDEX TERMSData mining, machine learning (ML), open data, smart city.
I. INTRODUCTIONA city is not only limited to physical urban spaces (e.g., places, and buildings) but also extends to systems, structures, networks, flows, and processes [1]. This is why Ahlers [2] defines a smart city as a livable, participative, and sustainable city. To develop such a city, open data produced by the different actors of the urban ecosystem play a crucial role [3], since their integration and valorization enable the development of high socio-economic impact services. The data are produced in a digital urban space that is composed of physical spaces (infrastructures, buildings, etc.), social spaces (government, population, organization, culture, etc.), and cyber spaces (internet data, communication data, etc.) [4]. The data are accessible through three main ways: official data portals (via the internet), big data initiatives (obtained explicitly or implicitly via crawling techniques), and the broader open data community [5]. However, not all open data are smart city-oriented. Prieto et al. [6] established 14 open data categories in the smart city to avoid ambiguity.The associate editor coordinating the review of this manuscript and approving it for publication was Sathish Kumar .