Resilient City: A Bibliometric Analysis and Visualization

Resilient city has attracted global attentions as a new concept for cities to deal with risks and challenges in recent years. Numerous researchers have successively conducted in-depth studies on the resilient city from different perspectives. To acquire an overview of resilient city and grasp the current research hotspots, a bibliometric analysis and visualization of the past decade of research on the resilient city was made.+e data were collected from 1249 articles published in theWeb of Science database from 2010 to 2019. As the widely used bibliometric analysis tools, CiteSpace and VOSviewer were adopted in this study.+e temporal distribution of resilient city research, including annual publication outputs and high-cited papers, was symmetrically analyzed. +en, the spatial distribution of resilient city research, including countries, categories, institutions, co-citation journals, author collaboration network, and author co-citation network, was investigated. Hot topics and evolution trends of resilient city were revealed. +e results show that the research of resilient city experienced three periods, namely, germination, rapid diffusion, and reflection and innovation periods. Current research focuses on four aspects, including psychological resilience at the microcommunity and group levels, assessment of urban disaster resilience, multiple theoretical frameworks of urban resilience, and urban resilience promotion strategy. +erefore, this study helps scholars and practitioners to gain a comprehensive understanding of the current research progress and evolution trends of the resilient city field.


Introduction
As a large and complex socio-ecological system, cities are characterized by concentration, mobility, integrity, and activity. City labels, e.g., low carbon city, eco city, green city, resilient city, and sustainable city, were used to briefly express essential features of urban development and construction goals. Cities are increasingly vulnerable to natural or artificial disasters due to large population, numerous building, and complicated social network. Resilient city construction has become an important issue during the global urbanization process. Research on the resilient city has attracted wide attentions from the academia and society.
ere have been abundant theoretical and practical studies in the world. erefore, a clear and systematic overview can help scholars form a comprehensive understanding of the resilient city research.
Resilience originated from physics and was used to describe the ability of an object to recover from deformation under an external force. en, resilience was introduced into ecosystems. Ecological resilience emphasizes the ability to adapt to external shocks and control interactive changes [1,2]. Subsequently, the concept of resilience was extended to the engineering technology and socio-economic fields. Engineering resilience focuses on the stability of the physical system, emphasizing its ability to recover to the predisturbance state [3][4][5]. In the social economy domain, psychological resilience [6], organizational resilience [7], and industrial resilience [8] were proposed from the perspective of the system level.
Due to complex internal factors and multiple external disturbances, cities have been suffering from a series of challenges, e.g., climate change, natural disasters [9], environmental pollution, disease transmission [10], and terrorist attacks [11]. Since 2002, the concept of urban resilience was presented at the American Annual Conference on Ecology [12]. e representative one, which was defined by the Rockefeller Foundation, refers to the capacity of individuals, communities, institutions, businesses, and systems within a city to survive, adapt, and grow regardless of chronic or acute shocks they experience [13]. Current research on city resilience mainly focuses on the system characteristics [14][15][16], construction [17][18][19], evaluation index system [20,21], and policy [22][23][24]. Although current studies are of great importance, the comprehensive overview on resilient cities' research is still lacking. e resilient city is a significant interdisciplinary research field, covering ecological environment, engineering technology, computer science, economics, social science, etc. To comprehensively understand the research progress and hotspots of the resilient city, it is necessary to conduct a bibliometric analysis.
Bibliometric analysis is a popular tool for scientific and technological text mining, which can quantitatively analyze the literature published in a specific field [25,26]. Mapping knowledge domain is a kind of graph that shows the relationship between the development process and structure of scientific knowledge. It can be used to grasp hotspots and frontiers of research in a certain field and make a panoramic representation by using its unique visualizations. Recently, bibliometric analysis tools, e.g., CiteSpace and VOSviewer, have been widely applied in various fields. CiteSpace can analyze node structure and characteristics, which usually works as an effective tool for researchers to extract network relations [27]. VOSviewer can provide detailed information about the literature, such as hot topics [28]. e objective of this study is to present a bibliometric analysis and visualization of the past decade of resilient city research. is paper is organized as follows. e first section describes the data source and methods. e second section shows the results of bibliometric analysis from six main aspects, namely, publication, subject category, country, institution, journal, and author. Finally, the hot research topics and emerging trends in the field are summarized.
Using the bibliometric analysis approach, this study explores the following research questions (RQ): RQ1: what is the overall publication trend and discipline distribution of resilient city research? RQ2: which authors, articles, journals, institutions, and countries have been most influential in resilient city research? RQ3: what are the hotspots and emerging trends in the study of the resilient city? RQ4: what recommendations or guidelines can be drawn for researchers of the resilient city field in the future?

Data Acquisition.
To obtain comprehensive and abundant literatures in terms of resilient city, Web of Science (WoS) was used as the data source. e Web of Science (WoS) online database contains almost all the important research papers, which also provides built-in analytical tools to generate representative data [29]. Detailed information, including publication year, country, author, institution, and journal source, was exported from WoS. e retrieval conditions were "resilience and urban," "resilience and city," "resilient and urban," and "resilient and city" to explore relevant theories and research contents in this field. e retrieval type was mainly keyword, and the time span was from 2010 to 2019 because the literatures on the resilient city were few before 2010. In total, 1249 valid literatures were obtained.

Methodology.
Developed by Professor Chaomei Chen of Drexel University in the United States, CiteSpace software is used to map and visualize co-occurrence networks and clustering in the research field, identify the coupling relationship between different nodes, and discover the knowledge characteristics in a specific period [30]. In this paper, CiteSpace was adopted to generate knowledge maps, including country, institution, author, journal, and references citation bursts (Section 3). VOSviewer, which was developed by Eck and Waltman, is an effective visualization tool that can be used to construct keyword mappings based on cooccurrence data [31]. VOSviewer was used to implement topic clustering (Section 4) in this study. e writing framework of this paper is shown in Figure 1. After the data were collected (Stage 1), visualization of research was made from temporal and spatial distributions (Stage 2). To be specific, temporal distribution analysis contains publication output and high-cited references. e spatial distribution analysis includes five aspects, i.e., country, category, institution, co-citation journal, and author collaboration network. Subsequently, hot topics and evolution trends were analyzed by the clustering and sequential analysis methods (Stage 3). Finally, conclusions and recommendations were presented (Stage 4).

Distribution of Annual Publication
Outputs. e amount of publications can visually present the research interest of a certain research topic in a specific period. e trend of publication outputs can provide an overall grasp of the research progress of the topic and play a strong guiding role in the development of future research.
rough the retrieval of articles in the field of resilient cities from 2010 to 2019, a distribution map of the publication output of resilient cities was drawn in Figure 2. Annual publication output in the resilient city field was 24 in 2010, and there was an overall upward trend from 2010 to 2019. e number of annual publications remarkably increased, and the maximum difference was 249 articles. Specifically, from 2010 to 2014, the number of publications on the resilient city grew slowly with an average annual publication volume of only 58. After 2015, with the acceleration of global urbanization and the surge of various natural and artificial disasters, the vulnerability of cities has become increasingly obvious. 2 Discrete Dynamics in Nature and Society   Discrete Dynamics in Nature and Society erefore, exploring the construction of the resilient city has become a significant path to achieve sustainable urban development. In 2015, the number of related papers began to grow substantially, exceeding 100 for the first time. In 2018, publication outputs reached the peak in the past decade, at 273. e average increase in the number of articles published in 2015-2019 was 45, which was 4 times that of 2010-2014. e quantity of publications issued in 2019 declined slightly, but it remained at a relatively high level. Obviously, the boom in resilient city research has formed in the past decade.

Distribution of High-Cited References.
e chronological distribution of articles is a time-series presentation in the dimension of research quantity, while the distribution of high-cited papers can be regarded as a time-series analysis in the dimension of research quality. e citation frequency of an article can reveal the influence and intelligence value of the article to some extent. Highly cited papers refer to academic papers that are cited frequently and have a long citation cycle. Papers with high citation frequency are usually regarded as authoritative and high-quality literature resources in this field.
is study used CiteSpace to count the top ten most frequently cited papers in Web of Science, which was ranked according to the frequency of citations, as shown in Table 1.
e first highly cited document is "Defining urban resilience: a review" written by Meerow Sara, published in "Landscape and Urban Planning" in 2016 and was cited 101 times. Based on a systematic review of the definition of the resilient city, this article summarized and put forward the connotation, extension, and characteristics of the resilient city and deeply revealed the nature and characteristics of the resilient city.
is article has become an important reference for multidisciplinary research on the resilient city [12]. e second high-cited article is a collection of essays on resilience research, which contains six subpapers. e authors explained resilience from different perspectives. Simin Davoudi discussed the significance of resilience and Keith Shaw raised questions about the politics of resilience; the third and fourth papers were published by L. Jamila Haider, Allyson E. Quinlan, Garry D. Peterson, and Cathy Wilkinson, both described the experience of integrating resilience into planning practice using examples from rural northern Afghanistan and urban northern Sweden; Hartmut Fünfegld and Darryn McEvoy discussed the main disaster management methods in climate change adaptation strategies and how to use resilience to change this situation; Libby Porter and Simin Davoudi raised some key questions about planning resilience [32]. "From fail-safe to safe-to-fail: sustainability and resilience in the new urban world" is the third highly cited article. It focused on the engineering field of urban resilience and proposed a set of strategies intended to build urban resilience capacity, including multifunction, redundancy and modularity, diversity (biological and social), multiscale network and connectivity, and adaptive planning and design to enhance the sustainability of urban development [33]. e fourth highly cited document "Planning the resilient city: concepts and strategies for coping with climate change and environmental risk" constructed an innovative conceptual framework: the resilient city planning framework (RCPF), which included the four related concepts of urban vulnerability matrix analysis, uncertainty-oriented planning, urban governance, and prevention. It also solved a key question of what cities and their communities should do to move towards a more resilient country in the future, which provides a comprehensive understanding of urban resilience [34]. From Table 1, the output of high-quality publications on the resilient city field was concentrated in 2010-2014, which indicates that the theoretical construction in the early stage provides a solid foundation for subsequent multidisciplinary research on the resilient city.
Burst detection is an effective tool to detect emergencies or major information within a certain period [35]. is article is titled "Resilience: e emergence of a perspective for social-ecological systems analysis" by Carl Folke. It integrated the concept of resilience into the study of socioecological dynamic systems, focusing on the sustainability of resilience in terms of governance capabilities such as renewal, restructuring, and development [36]. Norris et al. published the article "Community Resilience as a Metaphor, eory, Set of Capacities, and Strategy for Disaster Readiness" in 2008. Its citation burst intensity was 8.8638, which ranked second in burst intensity, starting in 2013 and ending in 2016.
is article proposed the theory of community resilience to provide strategies for disaster prevention from a microscopic perspective. e theory is based on four main sets of adaptive capacities, including economic development, social capital, information and communication, and community capacity [37]. In addition, it can be seen from citation cycle analysis that the longest citation cycle of the 25 highly cited references was 6 years, while the shortest citation cycle was only 2 years.

Distribution of Countries.
Using the national network analysis function in CiteSpace, the node type was set as "country" and the visualization map was optimized to generate a country distribution network map, as shown in Figure 4. e larger the circle, the more the number of publications. e thickness of the outer pink circle represents the size of centrality. e greater the centrality, the closer the connection with other countries and the more obvious the bridge function. e top 10 countries according to publication output are shown in Table 2. In general, there is a large gap in the research on the resilient city across countries. e United States is the first country to carry out research on the resilient city with the most studies of 284 (22.74% of the total). e United Kingdom followed behind with 149 (11.93% of the total). e average number of citations issued by the two countries is about 18, which is also at a relatively high level. is shows that they are two major countries in the field of resilient city research. e Dutch centrality is 0.7, and the average number of citations of published articles is about 24.75, indicating that the Netherland plays an important role in the overall research and acts as a knowledge intermediary and information flow controller.

Distribution of Categories.
In CiteSpace, "category" was taken as the network node and the time slice was set as 1 year. e co-occurrence map of the category network is shown in Figure 5. e larger the circle, the more the number of articles, and the thicker the connecting line, the closer the correlation. e complex connections established by multiple nodes indicate that the resilient city is a research field with significant interdisciplinary attributes. To further visualize the co-occurrence network map of categories, the annual distribution trend of the top 6 subject categories is shown in Figure 6. Among them, the most closely related category is environmental sciences and ecology with 412 articles published, accounting for 32.99%. e second-ranked category is urban studies with 262 articles, which accounts for 20.98% of the total. e engineering field is the third category of resilient city research. A total of 216 articles have been published, accounting for 17.29%. e top 6 categories also include other topics of science and technology, water resources, and public administration. It can be clearly seen from Figure 6 that, in the first stage of resilient city research (2010-2014), the resilient city study in various disciplines was in a groping stage and the number of publications fluctuated slightly on a relatively small basis. e resilient city research grew rapidly after 2015. e number of papers issued by the environmental sciences and ecology rose gradually and reached the peak in 2019. ere was an upward trend in other disciplines despite of the largest fluctuations in the engineering field. It should be noted that the attention of other disciplines in the field of resilient cities greatly weakened except the environmental sciences and ecology in 2019.

Distribution of Institutions.
e cooperation network of institutions was analyzed through setting the node type as "institution" in CiteSpace. Figure 7 shows the visualization map of institution in resilient city research. It is found that the connection between various institutions is loose. e cooperative networks have remarkable small group characteristics, e.g., King's College London and Arizona State University. However, single-line cooperation networks existed between most institutions. Divergent academic cooperation is still lacking in the resilient city field. erefore, it is necessary to strengthen the partnership between crossregional institutions and build a multicenter cooperation network. Top 10 productive institutions in resilient city research are shown in Table 3.
e institution with the largest number of articles is the University of Naples Federico II in Italy, with 20 papers. Institutions with more than 15 articles published include Arizona State University in the United States and the University of Melbourne in Australia. Seven universities, including the University of Exeter in the UK, Stockholm University in Sweden, the University of British Columbia in Canada, King's College London in the UK, Columbia University in the USA, the University of Cape Town in South Africa, and RMIT University in Australia have published more than 9 papers.

Distribution of Co-citation Journals.
e number of publications and the frequency of literature citations are important indicators for measuring journals in a research field. Table 4 shows the top 5 productive journals in the field of resilient city. "Global Environmental Change-Human and Policy Dimension" is the most prolific journal in the field of resilient city research (with 362 publications), followed by "Ecology and Society" (with 305 publications). It is worth noting that the top two journals have a higher total citation frequency at 6311 and 6169, respectively, which indicates that the two journals have higher reference value in the resilient city field than other journals. H-index, as an academic evaluation index, has now become an important criterion for journal assessment.
e H-index of "Global Environmental Change-Human and Policy Dimension" ranks first with a value of 147, which indicates that the articles included in this journal play a key role in the study of the resilient city. e average number of citations of a journal can reflect the overall quality of papers published in a certain journal. e articles published in "Ecology and Society" and "Annual Review of Ecology and Systematics" have high-quality characteristics, and the average number of citations of journal articles can reach above 20. e subject classification of five journals shows that the fields of ecology and environmental sciences have received the most attention.
e time-span presentation of cited journals in the field of resilient city research can reflect the outstanding contribution of the high-quality cited journals to the development of resilience urban. According to the time zone view of the co-citation journal in Figure 8 (node type: cited journal), the two journals named "Global Environmental Change-Human and Policy Dimension" and "Ecology and Society" took a leading position in the past decade. By 2011, the journal "Landscape and Urban Planning" received widespread attention and gradually developed into a key journal in the field of resilient city research. In the next few years, " esis" and "Sustainability" gradually attracted wide attention in resilient city research.

Distribution of Author Collaboration Network and
Author Co-citation Network. Using BICOMB2 software for calculation and analysis, a total of 3186 authors were found to participate in the research on resilient cities from 2010 to 2019. Price [38] defined high-yield authors in his book named "Little Science, Big Science." He believed "half of the , where i represents the number of works published by the most productive author, m is the minimum number of works published by core authors, n(x) refers to the quantity of authors who wrote x works, and N is the total number of authors [38]. After calculation, it is obtained that there are 136 high-yield authors in the resilient city research in the past decade, who published more than 3 papers (including 3).
According to Table 5, David Butler is the author who has published the most papers in the resilient city field, with 9 articles. is scholar is currently a professor in the field of water conservancy engineering at the University of Exeter in the UK, mainly engaged in water resources management, sustainable and resilient water systems, urban drainage systems, and other fields. e scholar constructed an overall resilience analysis method for urban drainage and supply systems, which can provide a flexible assessment of functional failures caused by unknown risk factors [39,40]. His research achievements have received extensive attention from the academic community. Leire Labaka is a new author in the research field of resilient city, whose most articles were published in the past two years. He mainly focuses on the resilience of urban key infrastructure and proposed a resilience maturity model, which provides an implementation roadmap for urban resilience construction and builds a public-private partnership framework for resilient cities Note that the symbols TC and TC/P refer to the total citations and the average number of citations per paper for a country, respectively. Discrete Dynamics in Nature and Society [41,42]. In addition, the authors who conducted extensive theoretical and practical research in the resilient city field include Josune Hernantes, Mark Pelling, and Eui Hoon Lee, who together constitute the core group of authors in the field of resilient city research. In Figure 9, the high-yield author's cooperation network map is presented to better display the knowledge cooperation of scholars in the field of resilient city research (node type: author). e nodes in Figure 9 represent authors. e larger the node, the more important the position of the author in the collaborative network and the greater the number of published papers. e lines mean that two authors appear in the paper at the same time, and the thicker the line, the closer the cooperative relationship. From the perspective of the overall cooperation network, the cooperation network density of authors in the field of resilient city research is 0.0044. Obviously, the network density is low, and its overall structure is relatively loose, indicating that the current knowledge and information dissemination and penetration in the field of resilient city research are weak. e breadth and depth of interaction between network nodes need to be further strengthened. e research team, which contains Takefumi Suzuki, Hiroyuki Uchida, Kenichiro Kubo, Masaru Mimura, Yasushi Imasaka, and Kazunari Yoshida, is the most prominent in the author collaboration network. e groups represented by Leire Labaka and David Butler both have a relatively high frequency of cooperation and extensive cooperative relationship. Figure 9 indicates that the academic exchanges between authors in the field of resilient cities need to be deepened. erefore, the field of resilient city in the future should focus on strengthening more extensive exchanges and communication among scholars.
By setting the "cited author" node, the co-cited author network graph is shown in Figure 10. e node represents the author, and the size of the node represents the frequency of citations. e thickness of the connection between the nodes represents how often the author is cited. e top 10 authors who are frequently cited are listed in Table 6. Holling C. S. is the most cited author (frequency 242 and centrality 0.29). As an expert in the ecology field, he first proposed the concept of resilience. Holling believed that ecosystems have two attributes, including resilience and stability, and specifically divided resilience into engineering resilience and ecology resilience, which promoted resilience research gradually from the field of natural ecology to the field of human ecology [43]. As one of the top 10 highly cited authors, the centrality of Holling C. S. is also particularly remarkable, which indicates that the author has laid a very important knowledge foundation for this research field and made outstanding contributions to knowledge dissemination. Ranked second is Carl Folke (frequency 237 and centrality 0.02), who systematically sorted out the evolution of the resilience perspective and gradually developed from the branch of ecology to social-ecosystem resilience [36]. e third place is Adger (frequency 173 and centrality 0.06), who comprehensively reviewed the fragility tradition and its evolution process. It is believed that vulnerability, adaptation, and resilience of the social-ecological system have common goals and foundations [44]. e author analyzed the significant correlation between ecological resilience and social resilience, which has attracted widespread attention from scholars in resilience urban research [45]. Others of the top 10 highly cited authors are Walker B., Cutter S. L., Meerow S., Davoudi S., Pelling M., Ahern J., and Berkes F.

Analysis on Hot Topics and Evolution
Trends of the Resilient City

Analysis of Hot Topics in Resilient City Research.
Keywords are the refinement and summary of the content of the article, and thus, the frequency analysis of keywords is usually used to reveal the research hotspots of a specific domain. In the case of numerous literatures and various keyword categories, the keyword co-occurrence map drawn by VOSviewer has the advantages of clear clustering, strong readability, and hard label overlap [31]. erefore, VOSviewer was utilized in this study to draw a keyword cooccurrence analysis map to present the distribution of hot topics in the resilient city research. In the VOSviewer, the threshold of word frequency statistics was set as 10. e first 120 keywords were selected to conduct keyword cooccurrence analysis of resilient city research in the paper, as shown in Figure 11. e size of the circle represents the frequency of keyword occurrence, the lines between each circle node represent the co-occurrence relationship, and the nodes with the same color represent the same clustering attribute. From the holistic perspective, "practice," "assessment," "measure," and "sustainability" appear frequently, which are hot topics in the field of resilient city. e hot topics of the resilient city can be divided into the following four categories:      Discrete Dynamics in Nature and Society   context of community is an early focus of urban resilience, which embodies the application of the concept of resilience in the psychology field. Community is the main unit of urban construction, and human beings are an important part of the urban system. ese studies believed that, in times of adversity, the leadership of individuals, the trust and support of the organization network, and the vision for the future are the significant factors for building urban resilience [46][47][48]. e high citation articles during this period focused on the psychological resilience and mental health of children or adolescents. Laura Camfield found that children with stronger social abilities were more likely to recover quickly from adverse experiences than children with personal abilities in developing countries based on a long-term follow-up survey of four adolescents in Ethiopia [49]. Due attention should be paid to developing children's social capacity to enhance psychological resilience. Fergus Stevenson and Zimmerman Marc A. conducted a study on adolescent psychological resilience at risk and discussed three elastic models, including compensation, protection, and challenge [50]. ey argued that parental support and personal social networking skills can help youth overcome risks and avoid negative outcomes.

Cluster #2 (Green): Study on Assessment of Urban Disaster Resilience.
e prime keywords are disaster, flood, earthquake, adaptability, assessment, method, uncertainty, recovery, indicators, etc. Natural disasters are the earliest area of concern for urban resilience. Research contents involve the construction of the  Discrete Dynamics in Nature and Society resilience capacity index system from the perspective of natural disasters, the experience reference of the resilient city case, and the discussion on the path of resilient cities to cope with natural disasters. e research of this cluster focuses on the capacity of urban infrastructure to withstand disaster risk. Hence, the construction of urban disaster recovery framework mainly pays attention to the features of facility redundancy, resource usefulness, and reflection when cities face risks. In 2003, Godschalk initiatively defined the resilient city from the perspective of urban disaster prevention and mitigation [18]. Additionally, he proposed a comprehensive urban disaster reduction strategy and considered that strengthening cooperation among professional teams and expanding urban systems research are important paths to build the resilient city [18]. Cutter et al. proposed the disaster resilience of place (DROP) model for communities to cope with natural risks, aiming to improve comparative assessments of disaster resilience at the local or community level [51]. León and March argued that the resilience in response to the tsunami can be enhanced by pooling regional urban resources through street networks [52]. Conducting the research on community parks in New York City under the impact of Hurricane Sandy, Chan et al. found that community parks not only strengthen food and ecosystem security but also play a crucial part in fostering community citizens' awareness of greening public spaces and social ecological restoration after disasters [53].
Cluster #3 (Red): Study on the Multiple eoretical Frameworks of Urban Resilience. e prime keywords are sustainability, landscape, urban systems, economic resilience, ecosystems, transformation, theoretical framework, etc. Resilience Alliance is one of the earliest organizations to conduct research on urban resilience. e alliance believed the research on the resilient city can be divided into four priority areas, namely, infrastructure environment, metabolic flow, regulatory network, and social level. In fact, it emphasized different emphases of the construction of the resilient city from the perspectives of economy, infrastructure, society, and ecology [54]. e Rockefeller Foundation put forward the City Resilience Framework (CRF) in 2014, which believes that a resilient city should include four main dimensions, including health and well-being, infrastructure and environment, economy and society, and leadership and strategy, with three specific driving factors in each dimension [55]. Desouza and Flanery believed that cities are composed of physical and social systems and cities need to resist natural, technological, economic, and human pressures through case studies [14]. Cutter et al. established a multidimensional resilience framework system for cities and communities to carry out resilience planning and evaluation for different subjects [17,51]. Cluster #4 (Blue): Study on Promotion Strategy for Urban Resilience from the Perspective of Social Governance and Urban Planning. e prime keywords are governance, government, practice, case study, food safety, green infrastructure, water resources, climate adaptation, housing supply, land use, etc. With the transition from ecological resilience to evolutionary resilience (social ecological resilience), the traditional "security defense" response strategy is no longer effective, and the "security free" strategy is exactly what is advocated in the modern construction of the resilient city [33,36]. Some scholars provided resilience as the core of the promotion strategy. For example, Ahern offered a suite of strategies intended to build urban resilience capacity, including multifunctionality, redundancy and modularization, diversity (biological and social), multiscale networks and connectivity, and adaptive planning and design [33]. Case study is a commonly used research method from the perspective of social resilience. rough the tsunami event in Chile, León and March believed that the design of the urban space and street layout can improve the resilience of a city to cope with the tsunami and thus summarized the strategy of planning resilience improvement [52]. Wardekker et al. took the specific city of Rotterdam as a case to put forward resilience strategies to deal with climate change and flood risk, aiming to provide a corresponding basis for the city's decision-making and planning [54,56].

Analysis on the Evolution Trend of the Resilient City
eme. CiteSpace was used to present the time zone map and emerging word view of the keywords in resilient city research, as shown in Figure 12 and Table 7, respectively. According to the generated time zone map, the research on the resilient city can be roughly divided into three periods, namely, germination, rapid diffusion, and reflection and innovation periods.

e First Period: Germination Period (2010-2011).
In the early years of this period, the theme of resilient city studies involved the psychological resilience of specific groups of human beings, mainly children and adolescents, with high frequency keywords such as adolescent development, community violence, resilience, protection, and African Americans. Meanwhile, with the development of ecological resilience in this field, the academic community has begun to pay extensive attention to the ability of cities to adapt to climate change. From the perspectives of ecology, engineering, and social politics, Kim and Lim presented a conceptual framework for analyzing urban resilience in the context of climate change, aiming to shed light on future urban planning and policies for adapting to climate change [57]. Similarly, Tyler and Moench proposed a framework of resilience to climate change, which includes the characteristics of urban systems, the agents (individuals and organizations) that rely on and manage these systems, the institutions that link systems and agents, and patterns of exposure to climate change [58]. e viability of the framework by the literature [58] was demonstrated through examples from 10 cities across Asia. Although the research literature on psychological resilience and ecological resilience dominated during this period, the resilience characteristics of urban systems began to attract attention from all sectors of society and generated research topics such as urban resilience planning, governance and transformation, sustainability, and management.

4.2.2.
e Second Period: Rapid Diffusion Period (2012)(2013)(2014)(2015)(2016). During the rapid diffusion period, resilience was applied to the functional construction of various subsystems of the city. Some themes related to urban resilience emerged, including community resilience, flood control resilience, critical infrastructure resilience, building environment resilience, earthquake mitigation resilience, and water resource resilience. e range of disciplines involved is increasingly wide, including energy, environmental science, engineering, geography, economics, management, and regional planning. Most of the multidisciplinary and multidimensional studies in this period focused on the construction of evaluation index system for different urban subsystems and the construction of the systematic comprehensive urban resilience framework.  (2017)(2018)(2019). During this period, the publications continued to increase. High-frequency keywords in this stage include green infrastructure, economic crisis, economic resilience, social resilience, urban resilience, sustainable development, and flood risk management. In addition to the diversity of research perspectives, there began to be some reflections on urban resilience paths and solutions, as well as the reconstruction of urban resilience indicators and theoretical framework. Kaika made a profound reflection on the construction of resilient cities, arguing that it would be difficult to make substantial progress if the resilient city study continues to adopt old methodological tools, institutional frameworks, and techno-managerial solutions [60]. Ziervogel et al. believed that the practice of resilience may be not consistent due to the difference in the development level between the global North and South, especially African cities, and proposed four entry points for integrating the right and justice into urban resilience [61]. Resilient city research is a dynamic and complex process from the perspective of the development needs of the city. Resilient city construction needs to pay equal attention to theory and practice.

e ird Period: Reflection and Innovation Period
e future trend of resilient city research is to put the research under the multilevel framework of environment, economy, society, and management, construct an operable Discrete Dynamics in Nature and Society   implementation framework, and formulate time-sensitive strategies for resilience improvement. e academic community believes that emerging technologies such as the Internet of ings, big data and cloud computing, artificial intelligence, and blockchain will serve as the development path for the construction of resilient cities. Smart technologies can provide a starting point in enhancing the city's disaster response, prevention capacity. and resilience of postdisaster recovery, which facilitate building a smart, safe, and resilient city. Importantly, smart, safe, and resilient city research is being highly focused, which has become the forefront of resilient city research.

Conclusion
Since the 21st century, the concept of resilience has been widely applied to the socio-ecological field and the research on resilient cities has shown a rapid growth trend. In this paper, CiteSpace and VOSviewer bibliometric softwares were used to analyze the temporal and spatial distribution of the research on the resilient city. Moreover, the research hotspots were revealed under the topic clustering of the cooccurrence network based on keywords. Finally, the thematic evolution trend of the resilient city was summarized according to the time zone distribution characteristics of keywords. e following conclusions were drawn: (1) e research of the resilient city presents the characteristics of multiscale, multidimensional, and interdisciplinary knowledge systems. In the context of different disciplines, the study of the resilient city has formed four aspects of subject clustering, including psychological resilience at the microcommunity and group levels, assessment of urban disaster resilience, multiple theoretical frameworks of urban resilience, and urban resilience promotion strategy. (2) According to the evolution trend of the theme, the research of the resilient city has experienced three periods, namely, germination, rapid diffusion, and reflection and innovation periods. With the adoption and application of the concept of resilience in various fields, the subject of research on resilient cities has become more and more extensive, from psychological resilience and ecological resilience in the early period to diversified research in different dimensions and processes in the social domain. e research issues have also expanded from the early restoration of natural ecology and spiritual level to urban regional planning, infrastructure construction, reconstruction of the built environment, water supply, and other issues.
us, the theoretical framework and evaluation system for the construction of modern resilient cities have emerged.
(3) From the perspective of co-authors and institutions, the research teams and institutions are relatively concentrated and the author cooperation network is loose as a whole. Knowledge dissemination and permeability are poor, and research cooperation depth and breadth are insufficient. e cooperation network shows fragmentation characteristics. In future research, scholars and institutions should break down barriers and explore cross-team, crossschool, and cross-regional collaboration. (4) In terms of the characteristics of the literature knowledge structure, the research on the resilient city is on the upsurge. e research methods are mostly theoretical, while the research from positivism is rare. e research focuses more attention on the construction of the theoretical system, and the practical exploration lags behind the theoretical analysis. Future research needs to combine theory with practice and carry out more cases and exploratory analysis.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that they have no conflicts of interest.