# Data Mining Algorithms for Smart Cities: A Bibliometric Analysis
## 2 Conceptual Framework
### Smart Cities  
In 2008, International Business Machines Corporation (IBM) proposed the new concept of the smart city [45] as the potential solution to the challenges posed by urbanization [21]. The term \"smart city\" defines the new urban environment, one that is designed for performance through ICT and other forms of physical capital [46]. The goal of a smart city is to provide citizens with a promising quality of life by using technology to improve the efficiency of services [47] and address inhabitants' demands [48] by optimizing its resources [49]. A smart city is conceived as an idealistic city, where the quality of life for citizens is significantly improved by combining ICT, new services, and new urban infrastructures [50]. [PERSON] [51] considers contemporary cities as repositories of images, movements, flows, and representations. It is important to emphasize that what ultimately makes the city \"smart\" is not simply data availability but the process of \"closing the loop\" consisting of sensing, communicating, decision making, and actuating [52]. [PERSON] et al. [53] consider the smart city as an adaptive system that can achieve two goals: support decision making and enrich the city domain knowledge. They represent the smart city operation in three phases, shown in Figure 1. During the first phase, real-time data streams are generated by hard and soft sensing. These data should be processed in phase 2 to gain useful information able to support decision making. During the third phase, knowledge is transformed into actions in the city. A smart city rests on people, technology, and processes and how they connect with various domains, including healthcare, education, transportation, telecom, tourism, utilities, public safety, and buildings. The characteristics of a smart city could be summarized to include six elements: Smart People, Smart Economy, Smart Mobility, Smart Living, Smart Governance, and Smart Environment (Figure 2) [50; 54; 55]. [PERSON] et al. [29] state that economic development, environmental issues, social equity, and sustainability for a smart city can be achieved only if all these aspects are equally considered. Figure 1: The three phases of smart city operation. Figure 2: The smart city pillars. The smart city is built on the infrastructure of the digital city. A digital city provides a 3D geospatial framework for cities, while the IoT embedded in the ubiquitous sensor network realizes real-time sensing, measuring, and data transmitting of still or moving objects [29]. The interaction of computational and physical components, specifically the use of cyber-physical systems, led to the advancement of such integration [30]. [PERSON] [56] uses the concept of \"programmable city\" as a prototypical code/space, where city functions are delegated to computational systems, which then renovate how they act. The term \"code/space\" articulates how the space phenomena translated into code that then acts recursively to alter them. The digital and physical cities are linked by IoT, thereby forming an integrated cyber-physical space. In this space, the state and changes in the real world will be sensed automatically in real-time [45]. In general, a digital city is a harmonious framework encompassing all kinds of information to ensure the city functions smoothly and orderly. Moreover, a digital city, as a considerable version of our real world, contains all the natural, social, and economic information related to the physical city [29]. The overall architecture of a smart city has a hierarchical structure of three layers [1], as shown in Figure 3:  
1. The \"instrumentation\" layer. The distributed sensor grid is embedded in infrastructure for acquiring and transferring real-time environmental and social data. Data acquisition elements are responsible for collecting and locally storing external data. It can capture any kind of information, including images, video, sound, temperature, humidity, pressure, etc.