1. Introduction

Recent literature on smart city infrastructure highlights the importance of digital and technological cities, and their ability to tackle various current challenges faced in urban areas, including traffic congestion, long commutes, lack of parking infrastructure, city sprawling, and public safety. When it comes to smart city infrastructure, recent literature on the subject highlights the importance of digital and technological cities in tackling various current challenges faced in urban areas [4]. Publications in the literature focus on very specific topics, such as smart roadway infrastructure [5], future visions [6], and blockchain for smart cities [7].

However, understanding smart cities’ infrastructure demands knowledge that accounts for technical, financial, and social constraints, as well as governance. It is also of prime importance to understand how these aspects are interconnected. This study’s novelty lies in presenting a classification framework that covers these aspects — technological, social, financial, and institutional — of smart city infrastructure.

There are several literature reviews on smart cities: some focus on digital systems [8], and some on the IoT technologies involved [9]. Other studies are concerned with technical standards involved in smart cities [10] and sustainable ways of implementing new urban systems [11]. Additionally, e-participation and e-government (and their role in making smart infrastructure) planning and operation have been described [12], as have innovations in artificial intelligence (AI), which recently gained prominence in the discussion of how to manage urban services and urban governance autonomously [13]. A comprehensive review on public-private partnerships (PPP) for financing and delivering smart infrastructure has also been presented [14]. Yet, many studies mainly outline opportunities and challenges without proposing a classification framework for smart city infrastructure research. This paper’s main contribution is the proposal of a framework, based on the literature, that identifies the close relationship between technical, social and governance-related aspects of smart cities’ infrastructure and connects that with the approaches, techniques, and challenges that are envisaged. A systematic flowchart of the conducted analysis was proposed, based on bibliometric and bibliographic analyses of smart cities’ infrastructure research. VosViewer software was used in order to create keyword clusters and identify the most influential key patterns in each scenario. A framework that highlights key themes and classes of research on smart city infrastructure conducted over the past eight years was presented.

2. Three Main Questions about Smart City Infrastructure

a. What are the various dimensions that smart city infrastructure research focuses on, and what are their associated frequent subjects?

There are three main focal points when it comes to smart city research dimensions: technology, community and institution (i.e., government) [127]. What can be noticed is that research articles tend to focus on one or two of these dimensions without regard to all dimensions. That means that most documents are either very technical (focusing on the technological aspect), or very social (focusing on how the government and the citizens are related to urban infrastructure). When it comes to review papers, this issue occurs less frequently.

For technology, the most prominent subjects seem to be sensor networks [105], IoT [108] and real-time traffic control [104]. It is important to note that the issues of big data and IoT seem to lack a broad perspective when it comes to smart city infrastructure, without cross-mapping and a clear initiative for implementation to go with proposed methods of addressing associated challenges. For the institutional aspect, the subject of e-governance and how it impacts decision making—in terms of infrastructure maintenance, operation and risk management—are hot topics in the realm of smart city infrastructure [128]. Nam et al. [129] conducted a literature review on the impact of blockchain technology on smart cities and discussed the major issues related to that technology, including some misconceptions. Krishnan et al. [84] reviewed several papers on e-government literature and assessed the mediation effects of the government’s willingness to implement electronic information sharing, electronic consultation and electronic decision-making, as well as the maturing relationships of e-government. Within the community focal point, e-participation and how it impacts decision-making for investment in smart city infrastructure is heavily studied, as are issues associated with boosting community participation in public life. For instance, Allen et al. [116] conducted a literature review about e-participation in monitoring service performance and open government, with a focus on citizens’ contribution to e-monitoring. Additionally, Yigitcanlar et al. [102] proposed a social media analysis approach that contained descriptive, content, policy, and spatial analyses. Recent studies have tended to focus on the technology and institutional dimensions, but there are subjects in all three dimensions that stand out.

b. What are the research themes and classes associated with these dimensions?

This research question’s main aim was to further filter down the dimensions identified in smart infrastructure research, based on a set of themes and interrelated classes of research themes. One of the fastest growing themes investigated is associated with smart city network architecture and transportation, with a large number of papers focusing on the state-of-the-art technologies implemented in smart infrastructure, operations management of smart infrastructure, and issues related to disaggregated infrastructure, traffic management, or mobility. Construction and governance are the next most highly active research themes, with emphasis on the following: ensuring sustainability in the construction of smart infrastructure; methods and approaches for linking ICT services to enhance governance of smart infrastructure; the notion of e-governance and its use for the operation and maintenance of infrastructure. It is also important to point out that many themes — e.g., energy, transportation, security, smart city network architecture, hydrology, construction, and land use — present papers that largely deal with the technological aspect, as follows:

• Energy-themed studies focus mainly on the smart grid [130], with articles tackling the issue of how to make the urban electricity system greener [131] and more efficient [132].

Security-themed studies focus on issues related to privacy, associated with infrastructure monitoring [133], methods of enhancing security of the infrastructure for the community via real time surveillance [134], and enhanced smart lighting at night time [135].

• Transportation-themed studies discuss traffic management via smart approaches [136], safety enhancement of the infrastructure system [137], and improving the operations of the system [138].
• Smart city network architecture covers papers regarding the installation of sensors throughout the city for diverse reasons [139], including big data analysis of urban systems to enhance their performance [140], communications technology, and mobile signal. There is also the issue of fragmented infrastructure [67].
• Health-themed studies focus on automated tools and technology embedded in the infrastructure for diagnosing defects, structural issues and maintenance requirements [141].
• As a theme, construction is associated with studies that target green construction of smart city infrastructure systems [111], along with the sustainability of the construction and maintenance of the systems [124].
• The land use theme focuses on studies that examine patterns of urban sprawl [142] and how to optimize smart infrastructure in saturated spaces such as densely habited urban areas [143].
• The hydrology theme covers studies that examine smart infrastructure water management systems [6] for clean water provision, sewage, sanitation, and drainage [115].
• The government research theme contains papers that examine e-governance of smart infrastructure systems [90], ICT services used to administer systems [144] and policy-making associated with systems [145].
• Lastly, under the population theme, articles that discuss smart communities (e.g., their participation in key decision-making regarding infrastructure systems, or enhancing their contributions via user-centric approaches) are categorized [146]. Studies that motivate citizens by utilizing transparent and accessible management models of smart city infrastructure are also grouped under this theme.

c. What are the main shortcomings of current approaches, and what would be a good research agenda for the future in smart infrastructure development?

A holistic view (involving all three dimensions of smart city infrastructure) is fundamental for a deeper understanding of smart city infrastructure. Some studies continue to focus on only one or two of the dimensions identified, while others fail to present a clear road map of technology implementation in smart city infrastructure that guarantees the involvement and consideration of the other two dimensions. This review of smart city infrastructure studies indicates that a possible blind spot continues to exist in ICT services, information systems, and e-government models available for smart cities. This may prevent unity within the infrastructure system, exaggerating Frankenstein urbanism in smart cities. For example, Cugurullo [119] discusses how smart cities fail to fulfill their philosophical and sustainable ideals, often replicating traditional capitalist urbanization strategies. Additionally, Yigitcanlar et al. [147] proposed that smart cities’ lack of progress can be attributed to strong techno-centricity.

The main shortcomings identified in the current literature are as follows:

• A more comprehensive understanding of the impacts of socio-technological practices on the future roadmap of smart city infrastructure development is needed.
• Most of the studies tend to focus on how to transform, ameliorate or create smart infrastructure and do not necessarily sufficiently tackle the issue of how to maintain and conserve it.
• Topics that collectively examine how smart infrastructure impacts economic growth and politics in the region are rare. There is an urgent need for studies that evaluate the realization of these aspects through quantitative comparisons or in-depth case analysis.

This entry is adapted from the peer-reviewed paper 10.3390/buildings11020073