Characteristics of Conceptually Related Smart Cities (CRSCs) Services from the Perspective of Sustainability

Abstract

A smart city has developed gradually with the evolution of services and ICT technologies to achieve sustainability. Many academic and governmental documents reference this; however, there is no existing theoretical or empirical study on the characteristics of smart city services regarding sustainability. In this sense, this study aims to clarify characteristics of Conceptually Related Smart Cities (CRSCs) services from sustainability. The methodologies adopt a matrix taxonomy to sort the previous indicators in the first step. It also utilizes a keyword analysis based on a literature review to identify the characteristics of two concepts. Three outcomes result from the steps of theoretical structures. Firstly, this study develops SSC service indicators based on the synthesis of Sustainable Smart City (SSC) and Smart City and sustainable city. The second outcome is an identification of the relation between SSC services and Conceptually Related Smart Cities. Lastly, the study clarifies the significance of citizen engagement based on the evolutionary concept by typifying service development in the lens of sustainability in CRSCs. This study is worthwhile for understanding smart city services and managing different featured smart cities from a sustainability perspective.

1. Introduction

Cities have developed services and technologies to achieve sustainability by satisfying each period’s issues and the various stakeholder needs. The city services and technologies have influenced cities and people in various ways depending on the regional characteristics, and on the other hand, they have been accustomed to cultural, social, environmental, and economic conditions. The contemporary society has developed various smart cities to achieve the Sustainable Development Goals (SDGs) by mobilizing frontier technologies and urban planning strategies.

The city services have been at the center of conversation in conceptualizing smart cities regarding sustainable development issues. According to the United Nations, the smart city is described as smart technologies for the sustainable community to achieve 17 Sustainable Development Goals and 2030 Agenda to ensure the principle of no one left behind (Excerpt from a chapter of “Transforming Our World” in 2030 Agenda for Sustainable Development Report (2016), and from The Sustainable Development Goal Report 2019). Since they published those two agendas, the UN has noticeably begun to transform our world. There are various urban service elements described, such as health (SDG 3), education (SDG 4), water and sanitization (SDG 6), energy (seg 7), economy (SDG 8), biodiversity (SDG 15), effective, accountable and inclusive institution (SDG 16) and partnership (SDG 17). They are dealing with physical environmental services at the same time, such as infrastructure (SDG 9), housing, public space, and disaster resilience (SDG 11), and natural environment (SDG 14). In other words, the SDGs address diverse aspects of services in terms of the social, human, and physical environment at each level of local, national, regional, and international prosperity, wellbeing, efficiency, and sustainability. City services, from the perspective of sustainability, have gained attention globally from academia and practice.

Many studies point out the correlation between sustainability and various smart cities leveraging Information Communication Technology (ICT). The service itself is mostly studied in the field of telecommunication. It is rare to find smart city studies to deal with urban services based on telecommunication technologies or ICT. Moreover, some municipalities develop the smart city to achieve local sustainability. However, they have either various names without considering urban service characteristics or a lack of consistency. Several cities entitle smart city projects with other equivalent names such as eco-city, digital city, intelligent city, ubiquitous city, and others even though they have general service characteristics at some point. Attaching similar names with the development of different services triggers confusion in further smart city development. It is basically correlated with the conceptualization process. Therefore, it is necessary to conceptualize the characteristics of different names equivalent to the smart city from sustainability by analyzing the different service developments.

This study aims to clarify the characteristics of Conceptually Related Smart Cities (CRSCs) services from the perspective of sustainability. For the study aim, the paper is structured as follows. Section 2 reviews the concept of smart city and sustainability and the existing literature on the sustainable smart city. Section 3 describes the methodology framework. Section 4 narrows down the study process and explains the three outcomes. The last section presents the concluding remarks.

2. Literature Review

2.1. Concepts of Sustainable Smart City

The concept of sustainability has adopted fundamental political principles since the publication of the Report “Our Common Future” (Brundtland Report) by the World Commission on Environment and Development in 1987 and the accomplishment of the United Nations Conference on Environment and Development (UNCED) in 1992 [1,2]. The sustainability for urban development has been highlighted after global agreements such as the United Nations’ Sustainable Development Goals (SDGs), 2030 Agenda, and New Urban Agenda in 2015. The urbanization and the rapid growth in urban populations pose new challenges for city services and infrastructure, but at the same time, it creates new economic opportunities and social benefits for people [3]. It triggers sustainable city indicators for international organizations and national and local governments, and many academic researchers.

However, the concept of sustainability is not a general or fixed term when it comes to the smart city field. Some authors define the Sustainable Smart City (SSC). Garau and Pavan (2018) assert that it needs to produce data, particularly given the city’s evolutive background in terms of energy and transport, and develop smart management strategies for using the cities’ resources more effectively and for decreasing the costs and waste that urban living generates, also in terms of wellbeing and inclusion in order to achieve sustainable smart urban quality [4]. Minako Hara et al. (2016) describe that the sustainable smart city should ultimately improve the city’s inhabitants’ quality of life through novel, more efficient, and increasingly inclusive ICT-enabled approaches [5]. Koichiro Mori et al. (2015) address that city sustainability denotes maximization of the total economic and social net benefits that a city produces, without exceeding environmental limits and staying within acceptable limits of socio-economic inequity [6]. Rahul et al. (2013) specifically describe it as a means for achieving a balance between the development of the urban areas and protection of the environment with an eye to equity in income, employment, shelter, essential services, social infrastructure, and transportation in the urban areas [7]. Adding to this, they assert that the sustainable index is necessary to achieve city sustainability. Sieting Tan et al. (2017) explain that a sustainable city needs the connections among social equity, economic productivity, and environmental quality to meet the present needs without compromising future generations’ ability to meet their own needs [8]. United Nations member states adopt the sustainable development goals (SDGs) to call to action to end poverty protect the planet, and ensure that all people enjoy peace and prosperity by 2030 [9]. ITU-T (International Telecommunication Union Telecommunication Standardization Sector) explains it as an innovative city that uses information and communication technologies (ICTs) and other means to improve quality of life, the efficiency of urban operation and services, and competitiveness while ensuring that it meets the needs of present and future generations concerning economic, social, environmental as well as cultural aspects [10]. The existing literature elaborates a sustainable city to develop specific urban services/elements while considering efficiency, social inclusion, active ownership, environmental resilience, and risk reduction to ensure no person and no place is left behind.

In this study, the sustainable smart city is a complex initiative for developing and implementing integrative urban service sustainably in social, technological, governance, environmental, and management aspects, extending Garau and Pavan’s (2018) concept and their way of developing methodologies.

2.2. Literature Review Regarding Sustainable Smart City (SSC) Services

A considerable number of studies dealing with smart city services have chiefly relations with sustainability in various aspects. Some authors describe ICT as a sort of tools to ensure an alignment of actors’ behaviors and visions to sustainability [11]. Souza et al. (2019) elaborate that smart cities promote economic development, improve their citizens’ welfare, and help people use technologies to build sustainable services through analyzing the smart city regarding data mining and machine learning approaches by conducting a systematic review [12]. Håvard Haarstad empirically examines the role of sustainability in the smart city discourse. His perspective on smart cities’ data shows that the smartness approach is strongly tied to innovation, technology, and economic entrepreneurialism. The smart city’s sustainability becomes apparent to the local level of the smart city platform. Caputo et al. (2018) identify the role of smartness for sustainability from the Smart Grid view. The advanced ICT technologies, including the Smart Grid, are crucial for activating urban sustainability [11]. Wong et al. (2020) have studied smart sustainable cities with the lens of blockchain technology in several areas such as governance, mobility, asset, utility, healthcare, and logistics to achieve social, environmental, and economic sustainability [13]. Suartika et al. (2020) describe the reason for technology-driven trends on smart city development by describing theories and origins of smartness and creativity. It adopts the sociopolitical dimensions with two other concepts of sustainable development and natural capitalism to go beyond metaphors of smart city and understand the discourse of smart city [14]. Regarding the social infrastructures such as stakeholder’s engagement and awareness, Lytras et al. (2018) cautiously analyze the citizens’ awareness of the smart city’s applications and solutions concerning the Sustainable Development Goal of no one left behind. The study has found the concerns regarding the utility, safety, accessibility, and efficiency of the services from the stakeholders. This study concludes that it could be manageable by interdisciplinary research [15].

Several studies explore the relations between smart cities and sustainability by adopting holistic approaches. Such approaches do not consider individual services; instead, they consider a smart city as a whole of elements by highlighting the integration of urban services and technologies. Some authors elaborate smart cities in a holistic approach by providing services layers with similar phases of seven-layer architectures in the telecommunication division. Anthopoulos et al. (2015) formulate the “n-tier architecture” containing natural environment, hard infrastructure, ICT-based infrastructure, services, and soft infrastructure through collecting information from literature and case studies. They conclude that a smart city needs to have various layers to be transparent [16]. Bifulco et al. (2016) found ICT and sustainability as across-the-board elements connecting with all the services provided to communities in the smart city. Specifically, the smartization process is enabled by sustainability and ICT as tools [17]. Nam et al. (2011) provide concepts of relevant terms with the smart city by categorizing the components into three dimensions: technology factors (digital city, intelligent city, ubiquitous city, wired city, hybrid city, and information city), institutional factors (smart community and smart growth), and human factors (creative city, learning city, a human city, knowledge city). The smart city has many fundamental components. The study conceptualizes the smart city concept as an organic connection among technological, human, and institutional components [18]. Deakin et al. (2011) describe four factors in a smart city, which is the application of electronic and digital technologies while using ICT to transform life and working environment as well as embedding of ICT in the government system, and lastly, the territorialization of practice to enhance the innovation and knowledge [19].

The evolutionary concept is an emerging academic discipline on sustainable smart city services. The holistic perspective based on technological evolution has influenced to drill on the process of developing smart city services, including its historical, theoretical, and ideological backgrounds. Although it has relative common ground with technological-driven and holistic approaches, it has distinctiveness in emphasizing urban services’ developing process. Mora et al. (2019) mention the fundamental role of ICT in the smart city concept to facilitate an innovative process in the services area and urban environments to accelerate urban sustainability. The emerging technologies prove their capability in facilitating the sustainable management of natural resources, ensuring equal access to essential services and infrastructures, promoting environmentally sound waste management and reducing waste generation, and improving the resilience of cities to natural disasters [20]. Anthopoulos studies the development phases of smart city services through a case study. The results show some service development types that some initial services commonly link to other services [21]. Estevez et al. (2016) illustrate in the United Nations University E-GOV (UNU E-GOV) report that smart city development refers to the continuous transformative process of building different services based on stakeholder engagement and collaboration. It contributes to improving its residents’ quality of life, achieving socio-economic development, and protecting natural resources [22].

There are some common elements in the relevant existing literature. They address either the phases of smart city services in a micro or macro perspective or the process of smart city services development based on the essential technological evolution. Most literature focuses only on the smart city itself except Nam et al. (2011) and Anthopoulos (2017). There is some academic discourse that suggests the smart city concept also comes from the confusion with other similar terms such as cyber city, intelligent city, digital city, and others [23]. Moreover, these terms refer to more specific and less inclusive levels of a city so that the concepts of smart cities often include them [19,24,25]. These trends show the necessity of the transparent and obvious research of identifying the relations of relevant terms with smart cities in service development views.

As this study aims to clarify the characteristics of the CRSCs services from sustainability, the gap from these smart city service studies can be organized into four topics: (a) developing SSC service indicators based on the synthesis of Sustainable Smart City (SSC) and Smart City and sustainability; (b) identification of relation between SSC services and Conceptually Related Smart Cities; (c) clarification of evolutionary concept through typifying service development in the lens of sustainability in CRSCs.

3. Methodology Framework

A matrix taxonomy and a keyword analysis are mostly utilized based on the literature review data to understand characteristics of the SSC services and CRSCs services in terms of sustainability, as shown in Figure 1. There are some steps to identify two characteristics. First, the indicators which imply the topic’s characteristics are compiled from the relevant literature review. In the compilation process, indictors are recommended to place on Y-axis, and the references are on the X-axis as the number of indicators is larger than the number of indicator groups. The second step is to sort the indicators and align them with the other five indicators to identify general terms. The respectively compiled lists overlap and collate the identical or similar word to the same row. They sometimes are converted to hypernyms or frequent words. The general terms are created by a synthesized process based on the other five indicators; this helps to identify indicators at a glance.

The next step is to extract the SSC services indicators. It is similar to Shen et al.’s (2011) study who replace indicators with some marks to compare them [26]. This study adopts a weighting system. The indicators get the weight based on their conformity; they will be assigned weight “1” if the indicator matches the general terms, which results from the synthesized process. Some will get weight “0.5” if they have similar meanings. Other would get “0” if the based indicators are omitted. The weight system communicates the result of how many respective indicators are included in the general term. The SSC service indicators are created based on the weight. In the complementation process, the SSC services do not include one if accumulated weights are less than three in the same row, for the reason that both Smart City and sustainability indicators need to synthesize more than average in reference to SSC indicators. In the meantime, the Sustainable Smart City Services includes some cases if they are only involved in the Smart City services indicators. The reason is that some particular indicators may solely have characteristics of the Smart City services. For example, data-related services have typically emerged in smart city services, reflecting current smart city development trends even though it has not been studied in terms of sustainability or the SSC. The weighting helps us to understand the indicators’ involvement. The synthesized process among five indicator sets allows for the creation of Sustainable Smart City Services indicators. The matrix taxonomy indicates the mostly included indicators and partially involved indicators in the stream of SSC, Smart City, or sustainability. For instance, the most mentioned indicators are shaded with dark grey. The light grey shading indicates the only element for the smart city services, as shown in Figure 1. The SSC indicators become the result of a combination of dark grey and light grey.

The fourth step is to analyze SSC services and apply them to CRSCs to identify the characteristics of the CRSCs. The keyword analysis, which focuses on the context of the keyword, is adopted to collect CRSCs data from relevant literature, encyclopedias, and white books, which result from Google Scholar, RISS, and encyclopedias based on the search keywords. As the keyword analysis is one category of content analysis, it also counts the number of keywords. However, it focuses more on the context as some English words have different meanings based on nuance and syntax, which means that the relevant concept sentences need careful observation. In other words, the Sustainable Smart City Services indicators are extracted from the written documents while understanding the meaning of sentences and the usages of words thoroughly. Then, the number of words in the documents is jotted down. When the most relevant literature is reviewed, the last (but not least) step is to analyze the matrix taxonomy and interpret the streams of numbers from the lens of sustainability and continuity. The interpretation process takes account of the first day of mentioning the CRSCs to realize the evolutionary concept in the holistic approaches. There are two service trends to be expected. One is continuous services regardless of transition phases and characteristics of CRSCs, and the other is the evolutionary trends in holistic approaches. The first one could be interpreted as the universal characteristics of smart city services, and the last one has a meaning of stepwise procedures based on service development phases. The detailed methodologies and outcomes are elaborated in the following chapters.

4. Results

4.1. Developing SSC Service Indicators

This study utilizes the matrix taxonomy based on thematic indicators shown as Figure 2, the study framework, to develop SSC service indicators. The research question of “What are the Conceptually Related Smart Cities service characteristics from sustainability?” operationalizes the unit of analysis and the SSC concept. As the CRSCs need to be identified from sustainability, the SSC is the larger concept of the CRSCs. The operational SSC concept in this study is defined through a literature review to decide the study population. The aforementioned SSC concept emphasizes smart city services development from social, technological, governance, environmental, and management sustainability. The CRSCs are thoroughly analyzed from the sustainable service perspectives per se. The CRSCs, which have a meaning of conceptually related terms, operationalizes the unit of analysis, which is the relevant written related with SSC, and the documents containing the concepts of CRSCs. This paper uses accepted academic papers chiefly and encyclopedia entries supplementally based on the objectives.

The concept SSC involves CRSCs, which are identified through investigating the indicators. The indicators often efficiently describe a specific country or city status by reducing the number of data obtained from multiple tools for various research methods into simple results or a single number while maintaining almost all the different content of each indicator [27]. Several studies conduct a literature review or synthesized bibliographical review to formulate composite indicators that efficiently describe specific topic characteristics. For instance, Girardi et al. (2017) aim to understand the assets that contribute to the operation of smart city services, estimate the benefit from the services, and identify the relations between service benefit and sustainability by utilizing synthesized matrix taxonomy [28]. Marsal-Llacuna et al. (2015) monitor the smart city initiatives based on the respective indicators of past and on-going initiatives in the field of sustainable cities and livable cities. The synthetic or aggregative index proceeds to visualize the initiative achievements [29]. Khansari et al. (2014) conduct a bibliographical review of the smart city and sustainability separately and then analyze the smart city impact on urban sustainability based on two literature reviews [30]. As many authors utilize the indicators to get to know the relations of the two terms, this study investigates the analogous indicators with SSC and identifies the SSC services by interactively comparing them. The initial step is to collect data from the existing literature, SDGs indicators published from United Nations, U4SSC published from The International Telecommunication Union (ITU), United Nations Economic Commission for Europe (UNECE), and sustainable smart city services indicators.

The reason for sampling those five indicators is described as follows. As few studies have been researched on the fusion of smart city and sustainability, many studies develop their indicators. Besides, the current indicators concerning the sustainable smart city or smart sustainability do not prove their reliability and validity. Additionally, their indicators have a different purpose with this study in terms that existing studies focus more on a specific theme such as energy, transport, or ICT technologies. This study measures the CRSCs services from a view of SSC framework by selecting the five indicators for this study purpose, which explores the CRSCs in the SSC boundary with holistic approaches based on the technological development theory. Therefore, the synthesis is appropriate for determining relevant academic boundaries and practical aspects to evaluate national conditions and standardize the worldwide SSC phenomenon.

For this reason, this study selects (a) the SDGs indicators, which are globally representative indicators for sustainability, (b) United for Smart Sustainable Cities (U4SSC), which is a UN initiative coordinated by ITU, UNECE, and The United Nations Human Settlements Programme (UN-Habitat) to achieve Goal 11, (c) SSC indicators extracted from the relevant academic papers, and (d) sustainable city indicators from the academic papers (e) Smart City services indicators from the academic papers. The relevant academic papers mentioned in (c), (d), and (e) are selected from Google Scholar. The inclusion criteria are whether they have keywords of “sustainable”, “smart”, and “service” in the title and whether they have organized relevant indicators. The exclusion criteria are the review study, which includes none of the relevant indicators or indexes.

Regarding the SSC indicators, Garau et al. (2018) organize 38 indicators under several categories: use and fruition, health and well-being, appearance, management, the environment, and safety and security [4]. Hara et al. (2016) propose 16 indicators under the environmental, economic, societal, and satisfactory categories [5]. U4SSC proposes 90 indicators under ICT, productivity, infrastructure, environment, energy, education, health, culture, safety, housing, and social inclusion pillars [31,32]. SDG indicators are a total of 115 in 17 goals. Regarding the sustainable city indicators, Tan et al. (2017) address twenty indicators in the categories of economy, energy pattern, social and living, carbon and environment, urban mobility, solid waste, and water [8]. Choon et al. (2011) elaborate on 30 indicators under economic efficiency, social harmonization, ecological balance, and management and environmental services [33]. Handryant et al. (2020) integrated 18 sustainability indexes with 29 sub-indicators and the categories of resources, nature, artifact building, impartiality/ fairness, security/safety, amenity, traffic/urban structure, growth potential, and efficiency/rationality [34]. Mori et al. (2015) visualize 12 indicators [6]. Alfaro-Navarro et al. (2017) suggest the 24 new sustainability city indexes of pollution, water consumption, water and recycling, land uses, labor market, GDP, health, safety, education, and culture [35]. Lynch et al. (2011) organize 17 sustainable urban development indicators for the United States with 51 sub-indicators grouped in environmental quality, social wellbeing, and economic opportunity categories [36]. Shen et al. (2011) compile 76 indicators under the categories: the geographically balanced settlement, the freshwater, wastewater, the quality of ambient air and atmosphere, the noise pollution, the sustainable land use, waste generation and management, health, safety, fire and emergency response, poverty, transportation, natural hazards, adequate housing, shelter, the security of tenure, access to credit, access to land, promote social integration and support disadvantaged groups, culture, recreation, availability of local public green areas and local services, participation and civic engagement, transparent, accountable and efficient governance, government, sustainable management of the authorities and businesses [6,8,26,33,34,35,36] The literature addressing smart city services is selected from the Google Scholar results using keywords of smart, city, and service models. The inclusion criteria are the literature published from urban-related journals, which means the technical-driven journals are excluded due to the study orientation. In addition, some literature containing duplicated indicators lists are excluded. The 19 pieces of literature are finally selected to establish Smart City indicators from the inclusion and exclusion criteria [10,21,23,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51]. The Smart City service indicators arrange into 14 indicators through reviewing and collating synonyms. The deducted Smart City service indicators are government and administration, transportation, environment, infrastructure, healthcare, education, economy, energy, safety, architecture, public, data collection tour, and waste.

After reviewing and organizing the relevant literature, the indicators are organized into a table by positioning the indicators on Y-axis and the references on X-axis. The indicators are aggregated and placed in the relevant cell, as shown in Figure 3. The indicators implying similar meanings could be allocated in the same row. The next step is to convert the list of indicators to the weightings of inclusion accordingly, shown in

Table 1. Conversion of Indicators.

Distinct Indicators for Sustainability	Sustainability		Sustainability + Smart City Service	Sustainability + Smart City		Smart CityService	Distinct Indicators for Sustainability	Total
	SDGs Indicators	Sustainable City Indicators	SSC Service Indicators	SSC Indicators	U4SSC	SC Service Indicators
	0.5	1	Security	1	0	1		3.5
	0.5	1	Safety	1	1	1		4.5
	1	1	Natural disaster	1	0	0		3
	0	1	Environment	1	1	1		4
	0.5	0.5	Environmental Quality	1	0.5	1		3.5
	1	1	Water, Sanitation	1	1	1		5
	1	1	Public Space, Nature	1	0	1		4
	0.5	1	Climate change	0	1	0		2.5
Biodiversity	1	1		0	0	0		2
	1	1	Economy	1	1	1		5
	0.5	0.5	Employment	1	0	1		3
	0.5	0	Finance	0	1	0		1.5
GDP	1	1		0	0	0		2
	0.5	1	Health	1	1	1		4.5
	0.5	1	Transport	1	1	1		4.5
	0.5	1	Governance	0.5	1	1		4
Area Management Cooperation with local community	0	1		0	0	0		1
	1	1	Waste	1	1	1		5
	0.5	0.5	Urban Planning	1	1	1		4
	0.5	0.5	Emotion wellbeing	1	0	1		3
	0	0	Social wellbeing	1	1	1		3
	1	0	Innovation	1	0	0		2
	0	0		1	0	0	Comfort	1
	1	0	Satisfaction	1	0	0		2
	0	0		1	1	0	Quality of life	2
	0	1	Efficiency	1	0	0		2
	0	1	Accessibility	1	0	0		2
	0	0		1	0	0	Flexibility and functionality *	1
	0.5	0.5	Housing	1	1	1		4
	0	1	Built environment	1	1	1		4
	0.5	1	Energy	1	1	1		4.5
	0.5	1	Education	1	1	1		4.5
	0.5	0	People	1	1	1		3.5
Stunting children	1	0		0	0	0		1
Sustainable Nitrogen Management Index	1	0		0	0	0		1
Yield gap closure	1	0		0	0	0		1
Distinct Indicators for Sustainability	Sustainability		Sustainability + Smart City Service	Sustainability + Smart City		Smart CityService	Distinct Indicatorsfor Sustainability	Total
	SDGs Indicators	Sustainable City Indicators	SSC Service Indicators	SSC Indicators	U4SSC	SC service Indicators
Gender issues	1	0		0	0	0		1
Victims of slavery	1	0		0	0	0		1
Compliance Observation of applicable laws	0	1		0	0	0		1
	0	0	History	0	0	1		1
	0.5	1	Culture	1	1	1		4.5
	0.5	1	ICT Infrastructure	1	1	1		4.5
	0	0	data	0	0	1		1
	0	0	Standardization	0	0	1		1
	0	0		1	0	0	Drainage	1
	1	0	Electricity Supply	1	0	0		2
	0.5	0.5		0	1	0	Food Security	2
	0.5	0		0	1	0	Agriculture	1.5
	0	1	Population	0	1	0		2
	0	0		0	1	0	Planet	1
	0.5	0		0	1	0	Prosperity	1.5
Press Freedom Index	1	0.5		0	0	0		1.5

Notes: SSC is an abbreviation of the Sustainable Smart City (SSC) in this paper.

. The matrix analysis for identifying SSC service characteristics consists of the indicators from the synthesized matrix taxonomy, which have included the matching terms weighted by “1”, similar meanings weighted by “0.5”, and those which have not been included were weighted by “0”. Those SSC service indicators are gathered into a category to see them at a glance. The SSC services indicators are extracted by selecting some weighted more than three from the accumulation of the five indicator’s weight. On the other hand, some also involve one of SSC services indicators if some Smart City service indicators are solely included. They are unique elements representing the Smart City service only without belonging to others: Data, Standardization, and History. They are highlighted with light grey in Table 1.

The five indicators are categorized into two tendencies. The sustainability tendency indicators are the SDGs and the sustainable city. The SSC indicators and U4SSC are in the SSC tendency indicator. It also includes the last indicator, the smart city service indicator, as it has similar SSC characteristics. There are comparable characteristics between the two tendencies, which are discussed in the following paragraphs.

The SSC service indicators result in 26 indicators. The indicators with more than average weight have similar weight on both tendencies. They are security, safety, natural disaster, environment, environmental quality, water and sanitation, public space and nature, economy, employment, health, transport, government, waste, urban planning, emotional wellbeing, housing, built environment characteristics, energy, education, people, culture, and ICT Infrastructure. They are related to urban services, physical environment, and ICT in the macro view. The social wellbeing indicator has, on the other hand, three weights from only SSC. Social wellbeing, which belongs to the community [52], is highlighted in the smart city project, which is more likely to deal with city size or community size. As it has a weight more than the average, it also considers one of the SSC service indicators. As mentioned above, history, data, and standardization are included as one of the SSC service indicators.

The SSC service indicators resemble the other three indicators mostly out of five. Among the 26 indicators, the SSC indicators and Smart City service indicators contain the most elements. The SSC indicators include 22, and Smart City service indicators involve 25. The SDGs indicators consist of five elements, which is the least number among five. From the total weight of similarity or the homogeneity, the range of the broadening concept is identified by comparing them. The SSC indicators, which gets a weight of 31.5 out of 52, has expanding concepts and a variety of characteristics. The sustainability city indicators occupy the second largest. The third one is SDGs indicators, which gets a weight of 26. The following one is U4SSC. The least elements are contained by Smart City service indicators. The outcomes of average homogeneity result in the fact that SSC service has similarity with Smart City. The individual homogeneity shows that SSC services are more related to the sustainability indicators since it is a broader concept. In short, the core elements of SSC service are matched more with the smart city at the extensive boundary with sustainability.

Table 1 describes the SSC characteristics from the perspective of sustainability. The outcomes of each indicators’ different characteristics apart from the common ones are what the counterparts lack. For example, the one shown only in the sustainability groups could be illustrated as the SSC’s lack in the view of sustainability tendency indicators. They are marked with bold black squares. The sustainability tendency indicators have distinct indicators, compared to the SSC indicators, which are biodiversity, GDP, area management cooperation with the local community, stunting children, sustainable nitrogen management Index, yield gap closure, gender issues, victims of slavery, compliance observation of applicable laws, and press freedom index. They can be summarized into four parts: citizen participation, social inclusion, future diversity, and GDP, which the SSC has not focused on. There are distinct SSC indicators: comfort, quality of life, flexibility and functionality, drainage, food security, agriculture, planet, and prosperity. They explain the smart city service characteristics from the perspective of sustainability. It correlates with many experts’ joint emphasis on the SSC that uses ICTS and other intelligent means to improve quality of life, the efficiency of urban management and services, and competitiveness while satisfying the needs of present and future generations [10,21,23,37,38,39,40,41,42,43,44,45,46,47,48,49,50,53,54,55,56,57,58] The private sector has been the leading developer at the beginning of smart city development and to date. It naturally reflects the result and vision of projects that focus more on functionality, efficiency, and quality of life. However, it needs to transform the directions to achieve sustainability. The sustainability would be accelerated by collaboration among various stakeholders, including private sectors, public government, citizens, and NGOs in order to achieve social inclusion and future diversity [59]

The United Nations states that “building partnerships with private technology companies, social entrepreneurs, academia, NGOs or international organizations can represent an effective way for Governments to make use of existing technologies to meet the needs of people and soften the impact of the crisis on their live … Partnerships between Governments, businesses and international organizations can also be crucial to maintain services for mission-critical communications and to ensure greater connectivity [59] (p. 224).”

Therefore, the multi-stakeholder partnership makes smart city services sustainable based on its previous characteristics, emphasizing quality of citizen life and efficient management of urban utilities and services functions.

4.2. The Relation between SSC Services and CRSCs

The synthesized SSC services indicators are utilized to identify the characteristics of CRSCs from the evolutionary concept based on technologically driven holistic approaches. The relevant city terms are based on the technological evolution which several authors introduce. Nam et al. (2011) elaborate on the smart city’s technological factor: the digital city, intelligent city, ubiquitous city, wired city, hybrid city, and information city [18]. Anthopoulos et al. (2017) flesh out the smart city evolution based on ICT development to treat local needs. They introduce the related terms, including cyber-based city, web city, virtual city, knowledge bases, broadband city, wireless/mobile city, smart city, digital city, ubiquitous city, and eco-city [21]. This study defines CRSCs as ICT-based evolutionary cities, including cyber city, virtual city, internet city, wireless broadband city, intelligent city, digital city, ubiquitous city, and smart city. Kim, N. (2020) assembles existing literatures on evolutionary theory to establish the theoretical background of exploring the CRSCs service development. This thesis paper visualizes the CRSCs services developments based on the cities’ plans [60].

The keyword analysis is adopted to sort the characteristics based on the SSC service indicators. The unit of analysis is the written documents dealing with the relevant city concepts searched from Google Scholar and RISS and encyclopedias based on each city name’s keywords. The keyword analysis draws out SSC service characteristics keywords by carefully exploring the keyword context, considering the sentences before and after the words. Additionally, it also takes into account the frequency of words as the method is one kind of content analysis. It simultaneously considers the meaning of the word qualitatively and the frequency of the word quantitively, which is different from the general matrix taxonomy. The qualitative observation is conducted to select the proper concept sentences from the documents. The number of similar and identical words are extracted and counted to identify their significance and continuity. The mixed methodology drives a more comprehensive and concrete understanding of the concept.

The first step is to aggregate the concept of CRSCs by reviewing the relevant documents. The databases are drawn from Google Scholar, RISS, and encyclopedias. Google Scholar has various kinds of abundant worldwide written documents, including conference papers, thesis papers, white books, reports, and journal papers, which help find the relevant material for some topics that have not recently been popular. The RISS contains a rich number of Korean papers more than Google Scholar. The encyclopedia is a common unit of social science analysis to locate implicit knowledge [61]. The exclusion criteria are the duplications, PowerPoint presentation, patent, book’s introduction, book review, and magazines. The encyclopedia is restricted to Wikipedia, Doosan, Maeil, and computer/IT-related sources. The inclusion criteria are the keyword entitled documents evincing the operational definitions and full paper structures. Consequently, the databases are established from 82 Google Scholar data, 20 RISS data, and 23 encyclopedia data.

After the screening, the full text that includes definitions and features is to extract and organize the concept sentences individually. The total number of collecting databases is 141 from the 125 written documents like Appendix A. The databases constituted 13 cyberspace data, 17 virtual city data, 3 internet city data, 8 wireless broadband city data, 9 intelligent city data, 12 digital city data, 14 ubiquitous city data, and 64 smart city data.

The CRSCs concepts are coded based on the 25 Sustainable Smart City services indicators. The matrix taxonomy consists of columns of the SSC services categories, SSC services indicators, the CRSCs characteristics, and other CRSCs in order from the left first column. The identical words or synonyms make sub-characteristics on the side of SSC indicators. The number of characteristics is counted and jotted down accordingly as in

Table 2. Comparison of SSC service indicators with Conceptually Related Smart Cities (CRSCs) services indicators.

SSC Service Category	SSC Service Indicators	Characteristics
Safe	Security	security
	Natural Disaster	natural disaster
	Safety	safety
Environment	Environment	environment, nature, green industry
	Environmental Quality	environmental quality
	Water and Sanitation	water and sanitation
	Public Space and Nature	public space
Economy	Employment	employment
	Economy	economy
		industry
		business
Health	Health	medical care, health
Transport	Transport	transportation
Governance	Governance	public portal to get information
		one stop service
Waste	Waste	waste
Vision	Urban Planning	control tower
		city development index
		holistic approach
		sustainable process of urban growth
		urban infrastructure, utility
		institution
		future city/new vision
		QoL/QoC
		welfare
		efficiency
		innovation
		creativity
		convenient, comfort
	Emotional wellbeing	cyber personal avatar, icon
	Social wellbeing	bridge digital divide
Architecture	Housing	housing
		home service, building
	Built environment characteristics	built environment characteristics
Energy	Energy	energy
Education	Education	many adults with a college degree
		learning, school, education
People	People	people, social inclusion
		local community communication
		human as urban resource
		socially citizen interact/involve
History	History	History
Culture	Culture	Culture
		consider nationality and locality differences
		tour
Hard Infrastructure	ICT Infrastructure	Backbone networking over city
		Information-based cyberspace as an infra, cyber rule
		information communication network
		access across city or district
		simulation, digitize or substitute reality
		collective intelligence, AI, creativity, intelligent organism
		embedded ICT into urban area
		monitor and integrate infrastructures
	Data	transparency and accountability of communication
		ITS, GIS, IBS, cloud, big data
		Information expression system
		Information network hard infra (device, computer)
		city function (work) implemented in a cyberspace
		manage information
		micro data and connection
		suggest or predict future
	Standardization	embrace flexibility on advanced technologies
		disappear of distance, life space is expanded, teleworking
		global communication
		Physical + Digital + Human system

. For the nonce words, the synonyms consolidate in a broad concept to a cell. For instance, government and administration are put in the same group as most urban administration on a large scale is correlated with the government.

Additionally, subcategory elements such as water, park, and sun could be involved in the environment. The economy includes business, marketing, and occupation. The total number of 65 characteristics are listed beside the SSC service indicators. All the indicators consist of more than one identical characteristic. It shows that the CRSCs characteristics are a more specific SSC services version, which includes entire characteristics.

The significant categories of CRSCs could be identified through the number of subcategories supporting the SSC service indicators. Overall, 20% out of 65 characteristics are involved in urban planning indicators. The ICT infrastructure and data accounts for approximately 12% of 66 characteristics; 6% of characteristics are positioned under the people and standardization category, while the others represent less than 5% of the characteristics. In this sense, many CRSCs characteristics affect urban planning, the data, and ICT infrastructure in a macro perspective.

The three significant categories, which are shaded in the Table 2, have relations to achieve sustainability. Well-planned urbanization ensures a sustainable and inclusive economy, society, and environment [62] The agglomeration benefits of urban planning reconstruct the policy’s intangibility into physical manifestations with the assistant of embedded ICT technologies, which connects different physical infrastructures by networking and disseminating information to the proper location [32]. In other words, urban planning enables the implementation of the policies with mobilizing the ICT. The ICT and open data can help collect and analyze microdata from personal usage of SNS (Social Networking Service) to the number and location of service institutions, geographical features, user feedback, or even available transportation network [63]. In this regard, urban planning is crucial for mediating the policy to implement and operationalize ICT features while the three elements are interactively conducted to achieve sustainability.

There has been a growing trend in urban planning to engage citizens in the process since the 1960s. The scientific and technocratic elites caused from industrialization and urbanization were replaced by a participatory and democratic shape for the advancement of sustainable development, the rapid growth of democracy and human rights, development concepts of civil society, and present cultural reactions interlaced with urban planning objectives [64]. Scholars and practices in this time are based on synthesized methods and principles of providing justice and social welfare [65]. Beyond the specific issue of suburban zoning, Paul Davidoff, a planner, and lawyer, developed the general concept of advocacy planning in 1965 based on “who speaks for the poor, the disenfranchised and the minorities?” [66]. He also states that the republican and democratic way of viewing city development should be a plurality of plans to support the private market and citizen engagement. The trend guides the technology adoption and advancement.

Urban planning guides the directions of ICT and data analytic technologies advancement in an appropriate way for all. Because the cities select appropriate smart city technology based on their urban problems and the urban paradigm shift holistically, the SSC is not transplanted from one geographic region to another. It needs to consider which value is essential for all in this time and place based on the participation of citizens who know the very detailed community and city events. According to advocacy planning, the unitary government does not know the specific local issues or encompass the individual public interest. The plan harnesses an enabling environment where laws and public policy protect and promote rights and responsibilities to mobilize community action to achieve social change [67].

4.3. The Characteristics of CRSCs

The outcomes indicate the continuous service characteristics from the grey and white cells in

Table 3. CRSCs indicators.

SSC Service Category	SSC Service Indicators	Characteristics	CRSCs Characteristics
			Cyber City	Internet City	Virtual City	Wireless Broadband City	Intelligent City	Digital City	Ubiquitous City	Smart City
Safe	Security	security							1	3
	Natural Disaster	natural disaster							1
	Safety	safety							3	8
Environment	Environment	environment, nature, green industry							2	14
	Environmental Quality	environmental quality							2	1
	Water and Sanitation	water and sanitation				1				3
	Public Space and Nature	public space						3	2
Economy	Employment	employment						2
	Economy	economy				1			2	17
		industry						2		2
		business						3	1	3
Health	Health	medical care, health							1	7
Transport	Transport	transportation							3	14
Governance	Governance	public portal to get information					1	3	2	1
		one stop service						1	1	1
Waste	Waste	waste								1
Vision	Urban Planning	control tower							1	2
		city development index								7
		holistic approach								1
		sustainable process of urban growth								18
		urban infrastructure, utility							3	8
		institution								3
		future city/ new vision	2				2		1
		QoL/QoC								5
		welfare							1	13
		efficiency								10
		innovation							2	6
		creativity					3			2
		convenient, comfort					1		1	1
	Emotional wellbeing	cyber personal avatar, icon	1	2	4					1
	Social wellbeing	bridge digital divide				4	2	2	f1	2
SSC Service Category	SSC Service Indicators	Characteristics	CRSCs Characteristics
			Cyber City	Internet City	Virtual City	Wireless Broadband City	Intelligent City	Digital City	Ubiquitous City	Smart City
Architecture	Housing	housing								5
		home service, building							3	7
	Built environment	built environment characteristics							1	1
Energy	Energy	energy								8
Education	Education	many adults with a college degree								1
		learning, school, education				1			1	7
People	People	people, social inclusion							1	22
		local community communication	3	2	1	3	2	4	2	4
		human as urban resource					2	2	2	3
		socially citizen interact/involve					1	5	3	4
History	History	History								1
Culture	Culture	Culture								2
		consider nationality and locality differences								2
		tour								1
Hard Infrastructure	ICT Infrastructure	Backbone networking over city	4	1	1	7	2	6	3	3
		information based cyberspace, cyber rule	10	2	3	2	1	6	2	3
		information communication network	3	2	6	6	4	5	5	8
		access across city or district				2	1	2	2	1
		simulation, digitize or substitute of reality	3	2	7		1	3	2	2
		collective intelligence, AI, creativity					5	4	4	13
		embedded ICT into urban area							5	8
		monitor and integrate infrastructures								3
	Data	Transparency, accountability of communication						2		1
		ITS, GIS, IBS, cloud, big data					1	1	1	1
		information expression system	2	2	4	1	1	2	2	2
		information network hard infra(device, computer)	4	1	7	3	2	3	4	5
		city function implemented in cyberspace			2		2	4	3	1
		manage information					1	2	5	16
		micro data and connection								7
		suggest or predict future								2
	Standardization	embrace flexibility on advanced technologies							1	10
		disappear of distance, expanded reality, telework	3				1	1	1	3
		global communication	2		1			2	1	4
		physical+digital+human system								8

. The CRSCs have three common characteristics: ICT infrastructure, data, and people from a macro perspective. In the ICT infrastructure, backbone networking over the city, information communication network, and information network hard devices are included in most relevant cities. It reveals that telecommunication networks and devices are essential in regard to the technology-driven perspectives. Regarding the people category, local community communication is a common characteristic. The CRSCs implement to the local community-oriented measures in their practical usage and purpose. The data equally include information network hard devices and information expression systems such as Bulletin Board System, WWW, and graphic data. Another essential service is the software or the contents through utilizing the hard telecommunication infrastructures. Those are the essential elements to develop a smart city regardless of its previous urban development stages. It could be summarized in three elementary services: information communication network with devices, people, and data with space for sharing contents. It implies that the CRSCs are evolved based on the three elements. In this regard, service evolution needs to be analyzed based on the history of internet evolution and people’s usage of such technology.

There are three phases of service development. The phases are the total number of characteristics in each city and the stream of service development. The characteristics of 41 elements are in the cyber city, 43 components are in the virtual city, 15 components are in the internet city, 34 elements are in the wireless broadband city, 38 items are in the intelligent city, 73 modules are in the digital city, 89 units are in the ubiquitous city, and 328 elements are in the smart city. The table has two transitions in developing services. The first one is shown in between the internet city and the wireless broadband city. The importance of emotional wellbeing via communicating user emotion changes into social wellbeing to bridge the digital gap.

Additionally, the trend is transformed from making the cyberspace simulation of reality expand the ICT infrastructures across cities or districts to reduce the digital gap. The other transition is revealed between the digital city and the ubiquitous city. There are many services that have emerged based on the previous services. For example, crime prevention, safety, environment, environment quality, employment, health, transport, urban planning, and others are newly created or consistently developed.

The first phase is the technological service development, which involves the cyber city, virtual city, and internet city. The three cities develop technological services focusing on hard infrastructure consisting of approximately 80% out of complete services. Their technologies have fewer varieties as they develop the same categories with common characteristics, even if the level of technology is different in the cities. The sole characteristics excluding the shared services over eight cities are sharing emotional conditions through icons, the eagerness of future cities with the new vision, and reflection of reality towards cyberspace in the belief of eliminating the distance between cyberspace and reality. The services mentioned earlier indicate that the unique social services are merely developed in the first phases. Instead, this stage develops the shared services focusing on technology.

The cities in the first phase have individual characteristics. The cyber city involves more standardization services and urban planning services comparatively. The virtual city focuses relatively more on data services among the three. There are no unique services in the internet city.

The second-phase cities, including wireless broadband cities, intelligent cities, and digital cities, tend to develop citizen-centric services. New services are emerging compared to the first phases, such as environmental, economic, people-centric, and educational services. Moreover, the cities in this phase produce many social inclusion services endeavors to reduce the social and digital gap by leveraging ICT and data analytic technologies. The technologies themselves are not the purpose, but they are the tools to achieve the society-related aims and solve the urban problems. In this phase, the urban planning focuses more on creativity and convenience on top of striving for the future city with a new vision.

There is still distinct service development in the second phase. The wireless broadband city solely develops water and sanitation service and economy service compared to the other two cities. The intelligent city focuses on urban planning. It also greatly influences service development to next phase cities regarding the setup of a public portal, people-centric development, some amalgamation technologies between reality and cyberspace, and manage city data technologies. The digital city has its characteristics such as transparency and accountability of communication and the significance of employment and publicity. It also becomes a starting point of some services concerning business and global communication.

The third-phase cities, such as ubiquitous cities and smart cities, tend to develop integrative and sustainable services based on local needs. This phase is an advanced one as even if the cities are organized in the same categories and mentioned in previous phases, it also integrates the previous two phases to achieve future sustainability by mobilizing effective advanced technologies and human-centric social services. Moreover, the newly implemented services consider the new paradigm shift, such as some visions of welfare and innovation in the ubiquitous city and some visions of Quality of Life (QoL) and efficiency in the smart city. Some urban services are added in consideration of local needs. The ubiquitous city adopts safety, health, and transportation service. Meanwhile, the smart city applies waste, housing, energy, history, and cultural services. It also adopts prediction services, microchipping data services, and integrative physical, digital, and human systems.

The characteristics of CRSCs are the service evolutions based on the previous technologies and surplus phases of service development. The three phases are developed based on the previous service and technologies. The table describes the advancement of technologies clearly through the increased block on the stack of previously developed ones from cyber city to smart city. The services, on the other hand, are hard to recognize at a glance. However, it could be identified through the gradually increased total number of services and the surplus phases of service development based on the previous services. Therefore, the CRSCs are in the evolutionary process with the three phases.

5. Discussion

The research question is “What are the Conceptually Related Smart Cities service characteristics from sustainability?” The research question is cast from the current issues on smart city implementation and study, emphasizing technologies and citizen participation without considering the paradigm shift or development context. Besides, many cities call smart cities by various names; this confuses the development of the concept. Therefore, this study aims to provide an insight into becoming SSC by adopting the evolutionary concept and analyzing the characteristics of CRSCs from the perspective of sustainability. The question was answered in three outcomes from each stage which is directly linked to the study gap. The three outcomes are a development of SSC service indicators based on the synthesis of related indicators, identification of relation between SSC services and CRSCs, and a clarification of the evolutionary concept by typifying service development in the lens of sustainability CRSCs.

The first outcome, which is a development of the hybridized indicator, reveals SSC’s characteristics as being different from the smart city and sustainability. The existing SSC service indicators are typically either synthesis of the sustainable city and the smart city in the lens of specific themes, or less involvement of city services with more inclination to a sustainable city, which results in the exploration of solely social, economic, and environmental factors. Garau et al. (2018) formulate indicators to evaluate the urban quality for the smart sustainable cities and apply them to measure a city case [4]. Hara et al. (2016) propose new key performance indicators based on the Gross Social Feel-Good Index to evaluate the smart sustainable city [5]. Although many papers just got to publish SSC service indicators, their themes are oriented to either a specific theme or synthesis of smart city and sustainability. Regarding the sustainable city, Tan (2017) deals with comprehensive indicators concerning carbon emission reduction to evaluate, implement and standardize Low Carbon City [8]. Mori et al. (2020) introduce a visualized model of City Sustainability Index (CSI), along with three pillars of sustainable development [6]. Alfaro (2017) develops an index based on the triple bottom line using an intellectual capital approach [34]. The sustainable city literature mostly deals with three pillars for sustainable development, excluding smart city indicators. On the other side, smart city papers mention sustainability as a vision in urban planning. They are more oriented to smart city services such as transportation, health, safety, education, and others. SDGs and U4SSC are representative materials for SSC. However, they have been merely utilized for analytic data even though there are many citations. Furthermore, existing literature tends to focus on specific themes, not a holistic view within the evolutionary theme. This paper is a first attempt to develop indicators by combining two practical global indexes, which are SDGs and U4SSC, with several academic indexes, which regard sustainable city and smart city, based on holistic perspective and evolutionary concept. The process provides distinctive characteristics of a smart city and sustainable city. The process brings a result of common ground, which is a newly devised SSC services indicator. The comparison between two groups with the common elements gives implications for the smart city implementation. The smart city services indicators are related to the joint emphasis of SSC and ICT, which are maintained by many scholars while containing contradictory visions which are the improvement of the QoL and development of the efficiency of urban management and service distribution, and the satisfaction of the needs of present and future generations. The smart city needs to transform its direction to achieve sustainability which is accelerated by a multistakeholder partnership mainly addressed in the sustainability city index group. Many private sectors do not welcome the sustainable concept, which lets them slow down in approaching the intended goals and intentionally implement business in the short-term and without sustainability [68]. However, the SSC service could be developed after the smart city implementation genuinely embraces the sustainability concept. It brings global prosperity to the present and future generations. Thus, the first study gap is to create new indicators based on the evolutionary theme for suggesting a way for current cities to become SSC for the development of diverse smart cities.

The second outcome is the identification of the relation between SSC services and the CRSCs. There is some academic discourse that the smart city also comes from the confusion with CRSCs [23]. The two existing studies provide the concept of the CRSCs. Nam et al. (2011) introduce the relevant cities concerning technology, institution, and human aspect [18]. Anthoupoulos (2015) describes it based on the date and plans of service implemented. They mainly focus on smart city service and implementation [69]. Besides, it is necessary to identify the CRSCs from the perspective of sustainability, current global and local agendas. This study compares CRSCs indicators and SSC services indicators. The three significant outcomes—urban planning, ICT, and data—explain why urban planning has crucial stances concerning sustainability. The agglomeration benefits of urban planning influence the policy’s issues physically with the assistance of ICT and Big data, connecting and managing the urban infrastructures, humans and nature [31]. There has been a growing trend in urban planning to engage citizens for an uprising of sustainable development since 1960 [64]. Paul Davidoff advocates that a planning method supporting the private market, and citizen engagement is a way to become both republican and democratic in his advocacy development [66]. Pereira et al. (2021) present SWOT as a simple, practical and accessible solution to enterprises to facilitate the integration of sustainability in each strategy [68]. Urban planning provides a way to become a sustainable development for ICT and data adoption by engaging citizens and private sectors. The second gap is to identify the CRSCs characteristics which are included in SSC services and discover the commonly highlighted three elements and their meaning.

The third outcome is to clarify the evolutionary concept by typifying service development with sustainability views in CRSCs. There are some discourses of SSC services as many scholars’ study smart cities concerning sustainability. One paradigm of SSC services is to utilize smart technology in order to achieve sustainability goals [11,12,13,14,70]. Some authors insist on services as a whole in holistic approaches. They attempt to build a model or architecture to take a snapshot of entire services [18,19,69]. A few scholars elaborate on the SSC services from an evolutionary perspective, highlighting the service evolution. It is developed based on the previous two disciplines. It also looks into the continuous process of developing services in a macro view based on the evolution of frontier technologies [20,21,22]. Among the evolutionary papers on SSC services, Anthopoulos solely takes a look at the CRSCs based on evolutionary phases of services with some city cases. In other words, the research has not been studied on the CRSC characteristics adopting evolutionary perspectives even though there are many smart city implementations under the goal of sustainability with various names. Therefore, this study gives conceptual guidance for developing a smart city sustainably based on continuous service evolution. It identifies three evolutionary stages on CRSCs. The CRSCs have been initiated by technological service development, and they tend to develop citizen-centric services. The third phase tends to develop integrative and sustainable services based on local needs. The evolutionary phases are similar to platform urbanism history at some points. The platform, which was first adopted as software by the computer industry in the mid-1990s, becomes a place for user-generated content (UGC) through blurring the lines between producers and consumers of digital content so as to anyone being prosumer. It has transformed into a web forum to interact with cultural and creative possibilities. It recently evolved into collective intelligence by combining the real world with virtual reality in a holistic way [71]. Thus, the third gap is that the analysis elaborates service evolutions’ phases based on the previous technologies and surplus of service development.

Generally, the three outcomes explain the significance of multi-stakeholder partnership for implementing sustainable smart city services. The CRSCs would become a multiplayer platform for confronting multiculturalism, where the needs have been changed in a timely and expeditious manner, through equipping ICT and utilizing Big data. The urban planning needs to be transformed into SSC urban planning by adopting the vision of the multistakeholder partnership in the CRSCs platform.

6. Conclusions

The cities have developed services regarding the urban issues in the period. Many recent cities adopt smart cities leveraging ICT to achieve sustainability. As the smart city has gained much attention from diverse stakeholders, similar terms are introduced without a definite general concept. Although their characteristics are different on service development, many cities and organizations indiscriminately have attached the diverse city label to all smart city projects. This phenomenon makes their characteristics blurred and ambiguous. In this sense, this study aims to clarify the characteristics of Conceptually Related Smart Cities (CRSCs) services from sustainability. The aim is specified through the research question of “What are the Conceptually Related Smart Cities service characteristics from sustainability?” In order to get the specific answers, the study framework is established by adopting matrix taxonomy and keyword analysis methodology. The new indicators are suggested reflecting the current trend, which is different from the existing SSC. The first methodology is utilized for establishing the Sustainable Smart City (SSC) service indicator, which is a newly created indicator by compiling five indicator groups: Sustainable Smart City indicators, United for Smart Sustainable City, Sustainable Development Goals indicators, Sustainability indicator, and Smart City indicators. The Conceptually Related Smart Cities (CRSCs) are drawn out from the related publications by utilizing the keyword analysis. Lastly, the characteristics of CRSCs result in three outcomes concerning SSC service indicators from the perspective of sustainability.

In conclusion, there are three outcomes in the process of achieving the study aim. The SSC service indicators are newly created. It is the first attempt to combine relevant global and local sustainability indicators with smart city service indicators, referring to the existing literature of sustainable smart city indicators. The indicator identifies the SSC characteristics from the perspective of sustainability, emphasizing the quality of citizens’ lives and efficient management of urban utilities and services functions. It also reveals the complementary aspects for the SSC, the multi-stakeholder partnership, to approach sustainability. The second outcome is that CRSCs is one element of SSC. The entire CRSCs indicators are involved in the SSC service indicators, which refers to the development of CRSCs as a sustainable process. Moreover, the two analyses of the sum of frequencies on each CRSCs characteristic and the total number of characteristics in each indicator indicate that both SSC and CRSCs put massive significance on the urban planning, ICT infrastructure, and data indicators. The three significant elements are correlated to achieve sustainability based on citizen participation. As urban planning plays a vital role by guiding the directions for ICT advancement and implementing the policy to the appropriate physical environment, it needs to set a goal for all in reference to advocacy planning. The last outcome is the characteristics of CRSCs from the perspective of sustainability. There are three phases of the CRSCs service development. It starts from technological-driven development and continues with citizen engagement development, and integrates the first two in the last phase in the holistic approaches. The characteristics of CRSCs are the service evolutions based on the previous technologies and surplus phases of service development. The three phases are developed based on the previous service and technologies. Therefore, it could say that the CRSCs are an evolutionary process in the boundary of Sustainable Smart City service development when it is explored in the viewpoint of sustainability.

There are some limitations even though the detailed analysis of SSC service and CRSCs are conducted with sophisticated structures. Firstly, like other literature review studies utilizing the matrix taxonomy, all relevant articles may not be included in the analysis. In order to minimize this risk, clear inclusion/exclusion criteria have been defined. Secondly, extracting keywords manually seems to be less systematic from the perspective of quantitative research. It could use quantitative methodology software to count the words. The Acrobat Finder function is additionally utilized for checking identical and similar words after extracting them qualitatively. The third is related to the omission of CRSCs keywords, which are mentioned in their literature. As this study focuses more on the cities based on technological evolution, it inevitably puts more weight on technologically related cities. The other CRSCs could be studied further with different study purposes. Lastly, the characteristics of a smart city could be changed as it is not a completed project but rather one that continually develops. In order to deal with these issues, this study transparently reports the data for further studies.

Nevertheless, this study provides a synthesized perspective via creating new SSC service indicators and suggesting a new evolutionary concept of CRSCs based on the SSC service development. The new indicators provide the foundation for evaluating and conceptualizing the upcoming sustainable smart cities. Besides, the three phases in evolutionary concepts of CRSCs could influence sustainable and continuous smart city development based on the services and local needs. Moreover, it prevents labeling the relevant terms indiscriminately and helps implementing projects strategically based on the different service characteristics.