Urban Quality: A Remote-Sensing-Perspective Review

Abstract

The assessment of urban ecological quality through remote sensing has gained prominence in recent years, due to the need for effective urban monitoring and improved territorial planning. This study presents a comprehensive review of the evolution of urban ecological-quality research from 1997 to 2023, focusing on trends, influential publications, and methodologies. From 1997 to 2023, research on urban ecological quality grew significantly, with annual publications increasing from 0.3 in the 1990s to six in the 2020s, driven by technological advancements, global collaboration, and alignment with policy goals like the UN Sustainable Development Goals (SDGs). Co-occurrence network analysis revealed six key research clusters, highlighting advancements in methodologies, spatial data integration, remote sensing, green sustainability, and multi-criteria frameworks, showcasing the field’s interdisciplinary evolution. China leads contributions, with 33.3% of research, followed by the United States and other countries, emphasizing robust international collaborations. Journals like Remote Sensing and Sustainability dominate, with highly cited publications from the 2010s and 2020s shaping the field’s direction. Prominent authors such as Xu H. and Zhang X. have played critical roles, though engagement in the field has surged more recently. Remote-sensing technologies, particularly in China, have been pivotal, with indices like the Remote-Sensing Ecological Index (RSEI) and its derivatives broadening analytical frameworks. These tools integrate ecological, socio-economic, and policy dimensions, aligning with global sustainability objectives and enhancing the field’s capacity to address urban ecological challenges and promote sustainable urban development. Urban ecological-quality research has evolved significantly, driven by advancements in remote sensing, interdisciplinary methods, and global collaboration. Future efforts should focus on expanding cross-regional studies, integrating comprehensive socio-economic and environmental indicators, and utilizing emerging technologies like machine learning, deep learning, and AI to address urbanization challenges and support sustainable development.

1. Introduction

The ecological environment is fundamental to human survival and development, encompassing the critical components, structures, and functions that sustain ecosystems [1,2,3]. Assessing and understanding the ecological quality of urban environments is pivotal for advancing sustainable resource use and addressing the challenges of increasing human pressures on global ecosystems [4,5,6] Evaluating and monitoring the ecological health and functioning of urban areas is crucial for developing effective strategies to mitigate the negative impacts of urbanization and promote more sustainable, resilient, and livable cities [7,8,9].

The increasing impact of human activities on global ecosystems threatens environmental resilience and sustainability [2,10,11,12,13,14,15,16,17,18]. As economies urbanize and advance, safeguarding the ecological environment through accurate monitoring has become crucial for effective governance and sustainable development [4,19].

Establishing an ecological civilization and achieving balanced socio-economic development are critical for sustainable progress [20,21,22,23]. The ecological environment is a fundamental factor in driving sustainable progress within society, encompassing diverse environmental elements that shape human activities, life, and the overall evolution of ecosystems [24,25,26].

Rapid urbanization exacerbates ecological challenges, highlighting the urgent need to reconcile urban growth with natural ecosystem preservation to promote sustainable development, especially in developing countries, necessitating harmonizing urban growth with environmental preservation [27,28,29,30,31,32,33,34]. This pressing need aligns with the United Nations Sustainable Development Goals (SDGs), particularly SDG 11, which emphasizes the creation of inclusive, safe, resilient, and sustainable cities [31,35,36,37]. To meet these challenges, robust and dynamic monitoring of urban ecosystems is essential [31,38,39,40,41,42]. In this context, the accurate and timely monitoring and evaluation of ecological conditions have become pivotal for informed regional environmental governance and sustainable development strategies [4,19].

Traditional ecological assessments relied on fixed-point observations and field surveys, which, despite their accuracy, were limited in spatial and temporal scope [43,44]. These methods were often resource-intensive and inefficient, limiting their ability to monitor large geographic areas or maintain long-term data continuity [43,44]. In contrast, remote-sensing technologies have emerged as transformative tools, enabling large-scale, continuous observations and providing comprehensive insights into urban ecological dynamics [45,46,47].

Assessing urban ecological quality through remote sensing is an established research field, with a history predating current developments [47,48,49]. These advancements have led to the development of robust indices such as the Remote-Sensing Ecological Index (RSEI), which form the foundation of urban ecological-quality assessments [7,50,51,52,53,54,55,56,57,58]. Despite progress in this field, gaps remain in understanding the integration of methodologies and the evolution of urban ecological assessments through remote sensing [59,60].

This research utilizes a mixed-methods review approach, employing bibliometric and elements of systematic analysis techniques to offer valuable insights into the research field of urban ecological-quality indicators. By combining mathematical, statistical, and literature analysis, the study presents a multi-faceted view of the evolution and impact of this body of work across various techniques [61,62,63,64,65,66,67,68,69,70]. This comprehensive understanding of research patterns and trends is essential for developing effective strategies to address urban ecological challenges, as it identifies critical areas for further investigation and highlights knowledge gaps [71,72,73,74]. Ultimately, this analysis seeks to drive continuous progress in assessing urban ecological quality through applying diverse methodologies and perspectives [31,72,75,76,77].

This study provides a comprehensive mixed-method literature review, incorporating elements of bibliometric and systematic approaches, to analyze the field of urban ecological-quality research with a specific focus on remote-sensing applications. It examines publication trends over time, identifying key patterns in the growth and evolution of the field, and evaluates the prominence of journals based on publication volume. The study further explores the leading countries contributing to this research and investigates the extent of international collaboration, highlighting global partnerships in the domain. Additionally, it identifies the main themes, focal points, and methodological approaches, with particular emphasis on the integration of remote-sensing technologies in urban ecological-quality studies. A geographical assessment of where these studies have been predominantly conducted is also included. By integrating these objectives, the review offers a clear and structured overview of the development, dissemination, and collaboration patterns that define urban ecological-quality studies and the pivotal role of remote sensing in advancing the field. The primary objectives include analyzing publication trends, identifying the most influential journals, and highlighting the country’s leading research output within this domain [61,62,63,64,65,66,67,68,69,70]. This analysis aims to enhance the understanding of urban ecological-quality assessments [31,72,75,76,77], offering valuable insights for advancing sustainable urban development [71,72,73,74]. Furthermore, the study explores the extent of international collaboration and examines the dominant themes, methodologies, and geographical focus of studies in urban ecological quality. By addressing these aspects, the paper seeks to uncover patterns that have shaped the research landscape and to identify emerging trends that could drive future advancements in this critical field.

By integrating diverse methodologies, investigating key contributors, influential publications, and evolving scholarly patterns, the paper offers practical insights to inform research and policy development. Ultimately, it seeks to bridge knowledge gaps and foster innovation, creating sustainable, resilient, and livable urban environments [31,72,75,76,77]. It proposes practical suggestions to guide future investigations and applications of remote-sensing technologies in urban environments. This review serves as a critical resource for identifying emerging trends and addressing knowledge gaps in urban quality, particularly emphasizing the role of advanced methodologies in remote sensing.

2. Materials and Methods

Our study employed a comprehensive and multifaceted methodological approach (

Table 1. This table offers a succinct overview of the linkages among the research questions, data sources, and analytical techniques employed in this investigation.

Questions	Analysis	Source Data
1. What are the patterns of publication trends in the field of urban ecological-quality studies?	General statistics	All papers
2. Which journals have the highest prominence, based on the quantity of articles published in the urban ecological-quality field?	General statistics	All papers
3. Which countries lead as producers in the scientific field of urban ecological quality?	General statistics	All papers
4. How extensive is collaboration between countries in the scientific field of urban ecological quality?	General statistics	All papers
5. What are the main themes, focal points, and approach utilized in urban ecological-quality studies?	Co-occurrence network	All papers
6. Where have these studies been predominantly conducted, geographically?	Reading and General analysis	Select papers
7. What are the patterns of publication trends in the field of urban ecological-quality studies?	Reading and General analysis	Select papers

). This involved integrating traditional bibliometric analyses with both qualitative and quantitative assessments, as well as elements of systematic review methods. We conducted a thorough examination of individual paper sections, to ensure precise information retrieval. By utilizing a diverse range of analytical techniques, we aimed to deepen our understanding of the subject matter. Furthermore, we carried out a co-occurrence network analysis to identify emerging trends related to advancements in urban ecological quality within the context of remote sensing. The detailed procedures for these methodologies will be presented in the subsequent sections.

Our study began with a well-structured approach. First, we selected the Scopus database as the primary source, as it offers comprehensive coverage and efficient tools for literature searches. We then carefully formulated a precise search query, identifying key terms relevant to the urban ecological-quality indicators domain. This allowed us to retrieve a targeted dataset. To further refine the information, we filtered out non-peer-reviewed publications, such as reviews, conference proceedings, book chapters, and books. By focusing solely on articles published up to 2023, we were able to avoid potential duplication of content across multiple publication sources, ensuring the accuracy and reliability of our research (Figure 1).

Following the creation of the refined dataset, we initiated a meticulous manual screening process to ensure the relevance and accuracy of the selected papers. This phase involved applying specific selection criteria to identify studies that aligned with the objectives of our research. The criteria included papers that had a central focus on employing remote-sensing techniques for the description and evaluation of urban quality, as well as those utilizing spectral indices, or their combinations, for this purpose. Titles and abstracts of all identified papers were carefully reviewed, to confirm their relevance to the investigation of urban ecological-quality indicators. In cases where the relevance was unclear from the title or abstract, the full text of the paper was examined, to ensure alignment with the study’s objectives. This rigorous and systematic screening process was essential for maintaining the precision and reliability of our findings while building a robust dataset that supports meaningful analyses in the context of urban quality evaluation through remote-sensing techniques.

To analyze trends in the literature on urban quality with a remote-sensing approach, we focused on identifying dominant contributions and influential patterns within the field. For this purpose, we prioritized the most-cited papers over time, comprising approximately ~77% of the total dataset, equivalent to 34 papers. This representative selection provided a solid basis for capturing key trends and influential works shaping the research landscape.

During this phase, we extensively analyzed the selected literary dataset. This analysis included overall statistical summaries, country-specific scholarly output, network analysis of co-occurrences, publication trends over time, author productivity changes, and international collaboration efforts. The review process entailed a comprehensive examination of each publication, with precise documentation of essential details such as the type of urban ecological index used, the variables assessed, the country of the study, whether the research compared patterns across three distinct periods, the sensor system employed, and the geographic location of the investigation.

Focusing on the most-cited articles and documenting their methodological and thematic contributions allowed us to capture key drivers and advancements in the field, ensuring a robust and meaningful evaluation of trends in the literature.

2.1. Data Base

The research methodology employed in our study was comprehensive and multifaceted, involving a combination of traditional bibliometric analyses, qualitative assessments, and quantitative evaluations, as well as elements of systematic review techniques [61,64,78,79]. This approach enabled us to gain profound insights into the most influential research within the field [79,80]. In commencing our study, we meticulously chose Scopus as the primary database, due to its comprehensive features and benefits. Established in 2004 by Elsevier, Scopus is a multidisciplinary bibliographic database offering extensive coverage of international scientific literature. Boasting over 53 million references from more than 24,000 scientific journals dating back to 1996, Scopus provides a wide-ranging reach. Moreover, it furnishes various tools to facilitate efficient and targeted literature searches, enabling researchers to utilize primary- and advanced-search functionalities [81]. These capabilities expedite information retrieval, providing a thorough perspective across various scientific fields [81]. Considering these notable advantages, the research team determined that Scopus was the most suitable database for the literature review conducted as part of this study [81].

2.2. Query String and Screening Process

The construction of the search string in our study was methodically designed to ensure comprehensive coverage of the relevant literature, while maintaining precision and alignment with the research objectives. The process began with decomposing research goals into topic phrases, which were further distilled into specific search terms. For instance, the objective of assessing urban ecological quality led to the inclusion of terms such as “urban ecological quality” and their derivatives. Synonyms and related terms were incorporated to broaden the scope and enhance retrieval accuracy. To achieve this, an iterative process was employed, wherein initial search results were analyzed to identify commonly used terms and concepts, which were then integrated into the search string. Boolean operators and wildcards were employed strategically to capture variations in terminology and ensure inclusivity, reflecting the diverse ways researchers describe urban ecological-quality phenomena.

For this study, we used the following search query to capture the most accurate and pertinent results: TITLE-ABS-KEY ((“Cit* quality” OR “Cit* indicators” OR “Cit* sustainable” OR “Cit* ecological quality” OR “Cit* ecological index” OR “Cit* ecological quality indicators” OR “Cit* ecological resilience” OR “Urban quality” OR “Urban indicators” OR “Urban sustainable” OR “Urban ecological quality” OR “Urban ecological index” OR “Urban ecological quality indicators” OR “Urban ecological resilience” OR “Urban sustainability quality” OR “Urban sustainability index” OR “Urban sustainability indicators” OR “Urban ecological resilience” OR “Urban sustainability resilience”) AND (“remote sensing” OR “satellite imagery” OR “geospatial”)) AND PUBYEAR < 2024 AND (LIMIT-TO (SRCTYPE”,j”)) AND (LIMIT-TO (PUBSTAGE”,final”)) AND (LIMIT-TO (DOCTYPE”,ar”)).

This search query was applied to the Scopus database to ensure precise and comprehensive identification of studies relevant to urban ecological quality that were aligned with our research objectives. Initially, titles and abstracts of all retrieved articles were systematically reviewed to confirm their thematic relevance. For articles with uncertain relevance, a full-text review was conducted to ensure their inclusion in the dataset was appropriate. To maintain focus on rigorously vetted research, gray literature, review articles, conference proceedings, book chapters, and books were excluded. This exclusion criterion ensured that the dataset was comprised solely of peer-reviewed journal articles published in their final form up to 2023, reflecting the field’s most relevant and authoritative contributions.

The data processing framework was structured to enhance dataset quality and analytical value. Articles were categorized by publication year, to identify temporal trends, and research themes, to uncover thematic patterns and methodological focus. High-citation articles representing key contributions to the field were prioritized for deeper analysis. Rigorous filters were applied to eliminate duplicates, ensuring the uniqueness of each entry. Metadata integrity was verified by checking author affiliations, publication sources, and keywords to confirm consistency and reliability. These steps ensured that the dataset was comprehensive and precise, forming a solid foundation for subsequent analyses.

Each selected article underwent further assessment to evaluate methodological rigor, including the application of remote-sensing technologies, choice of evaluation indicators, and geographical scope of the research. This process facilitated a nuanced understanding of the methodological landscape and its evolution in urban ecological-quality research. Moreover, the dataset identified key thematic clusters and collaborative trends, offering insights into how the field has developed.

2.3. Data Analysis

We conducted a comprehensive analysis of the scientific literature, employing a methodology leveraging quantitative tools and advanced visualization software. All data processing and statistical analyses were executed using R version 4.0.4 [82,83], the RStudio IDE version 1.4.1106 [84,85], and Ggplot2 version 3.3.5 [86], ensuring a rigorous and reliable examination of the dataset.

We use the Bibliometrix package [66] to perform quantitative analyses. The Bibliometrix package represents a robust statistical tool designed explicitly for scientometric and bibliometric analysis, and was used to extract detailed insights from the literature. This tool allowed us to analyze various dataset dimensions, including author productivity, scientific output by country, international collaborations, temporal trends, co-authorship patterns, and the impact of highly cited articles.

To complement these analyses, we employed VOSviewer 1.6.20, a specialized software for visualizing and analyzing bibliometric data [67,68,70,87,88,89]. Using VOSviewer’s “map based on text data” feature, we constructed co-occurrence networks by integrating data from the selected papers titles, abstracts, and keywords. The bibliographic database files were processed using a binary counting algorithm, and a synonym file was created to correct semantic errors caused by redundancy. A minimum threshold of two occurrences was applied while constructing the co-occurrence networks, to ensure the inclusion of relevant terms. This approach enabled a comprehensive visualization of the dataset’s relationships between key terms and concepts.

Additionally, we systematically evaluated all papers identified during the screening phases, to ensure data integrity. Each selected paper was meticulously reviewed to confirm that all extracted data were directly derived from the original articles. This rigorous process ensured the reliability and accuracy of the findings, allowing us to gather detailed insights for further analysis.

Our methodology provided a cohesive and multidimensional dataset analysis by integrating the capabilities of Bibliometrix and VOSviewer with systematic evaluation methods. This logical and structured approach ensured that each step of the research was interconnected, enabling a thorough and reliable examination of the scientific literature in the field.

3. Results

3.1. Production Trends

The examination of publication trends in urban ecological-quality research from 1997 to 2023 highlights a profound evolution in the field, characterized by substantial growth in research output, collaboration, and technological integration. While the 1990s and 2000s experienced modest publication rates—averaging 0.3 and 0.4 papers annually, respectively—the field witnessed a transformative surge in the 2010s, with an average output of 1.5 papers per year (±2.27). This upward trajectory continued in the 2020s, reaching an average of approximately six papers per year (±3.36). The most prolific years—2023, 2021, 2022, 2018, and 2019—saw publication peaks of eight, eight, seven, seven, and four papers, respectively, underscoring a distinct acceleration in research activity. This increase is closely linked to advancements in computational tools, sensor technology, and remote-sensing methodologies, enabling researchers to explore urban ecological systems with unprecedented precision and depth (

Table 2. The table provides a comprehensive overview of the quantitative aspects surrounding the publication sources, authors, and collaborative networks that have shaped the research landscape on urban ecological quality over the decades.

Timespan	1997:1999	2000:2009	2010:2019	2020:2023	1997:2023
Sources (Journals)	1	4	14	19	35
Papers	1	4	15	24	44
Annual growth rate %	-	-	-	-	8.33
Papers contents
Authors
Authors	1	12	47	102	156
Authors of single-authored docs	1	0	2	0	3
Author collaboration
Co-authors per doc	1	3	3.47	4.8	4.14
International co-authorships %	0	0	13.3	16.6	13.6

).

The growth observed since the late 2010s aligns with the broader adoption of emerging technologies, such as machine learning algorithms, and high-resolution remote-sensing instruments. These advancements have revolutionized data collection, processing, and analysis, facilitating the development of more comprehensive and integrative urban ecological frameworks.

Furthermore, expanding publicly available geospatial data and the increasing use of cloud computing platforms have made large-scale ecological analyses more accessible and scalable. These technological drivers and heightened policy interest in urban sustainability—particularly in alignment with the United Nations’ Sustainable Development Goals (SDGs)—have propelled the field forward. For example, SDG 11, which focuses on sustainable cities, has galvanized research to improve urban ecological resilience and sustainability through innovative methodologies.

The rise in collaborative efforts has further fueled this growth. Between 2020 and 2023, the number of contributing authors peaked at 102, significantly increasing from 47 in 2010–2019 (Figure 2; Table 2). This surge in collaboration is reflected in co-authorship rates, which increased from an average of 3.47 authors per paper in the 2010s to 4.0 in the 2020s. Moreover, the percentage of international co-authorships reached its highest levels during 2020–2023, signifying the development of a global research network in urban ecological quality. The reversal of declining co-authorship trends observed in the previous decade underscores research partnerships’ dynamic and evolving nature. This global interconnectedness fosters the exchange of diverse perspectives and strengthens the field’s capacity to address complex challenges posed by rapid urbanization.

Overall, the 8.33% growth rate in publication output from 1997 to 2023 reflects the increasing importance of urban ecological quality as a critical study area (Table 2). Technological innovation, international collaboration, and policy-driven research agendas have driven this growth. The findings highlight the field’s maturation, as evidenced by its methodological advancements, thematic diversification, and establishment of a global research community. These trends underscore the critical role that urban ecological-quality research plays in addressing pressing environmental challenges and shaping sustainable urban futures.

3.2. Co-Occurrence Network Analysis

The co-occurrence network in Figure 3 offers a detailed representation of thematic clusters and their interrelations within the field of urban ecological-quality research. These clusters, derived from 190 elements, reflect the diverse approaches and methodologies employed in the domain, revealing the key focal areas that have shaped the field over the past 26 years.

The six thematic clusters in the network demonstrate distinct research trends and thematic overlaps, offering valuable insights into the field’s evolution.

Cluster 1, the largest cluster, consists of 47 terms and emphasizes methodological advancements, particularly in developing ecological indices such as the Remote-Sensing Ecological Index (RSEI). Key terms include “ecological quality”, “quality indicator”, and “remote sensing ecological index”. This cluster underscores the role of advanced quantitative tools and models, such as Principal Component Analysis (PCA), in analyzing urban ecological quality. The prominence of these tools reflects the growing demand for robust frameworks to evaluate urban environments, enabling researchers to assess ecological health with precision and consistency. The emphasis on these methodologies also demonstrates the field’s move toward data-driven approaches supporting evidence-based urban sustainability policy-making.

Cluster 2 focuses on cartographic modeling, mapping techniques, and integrating spatial data for environmental monitoring. With 35 terms, this cluster highlights the critical role of spatial visualization techniques in understanding urban ecological dynamics. Dominant terms like “mapping”, “spatial distribution”, and “urban planning” reflect the increasing reliance on Geographic Information Systems (GIS) and related tools for capturing spatial heterogeneity. These tools are instrumental in modeling urban landscapes and identifying priority areas for intervention, facilitating more effective urban planning strategies.

Cluster 3, comprising 33 terms, emphasizes the applications of remote-sensing technologies and their relevance to policy and decision-making. Terms such as “remote sensing”, “policy maker”, and “decision maker” dominate this cluster, indicating the significant role of satellite imagery in addressing urban challenges like land-use change, urban sprawl, and ecological degradation. This thematic area underscores integrating high-resolution remote-sensing data with urban ecological frameworks to inform actionable policies. It highlights how data-driven insights are increasingly used to bridge the gap between scientific research and practical urban management, ensuring decision-makers have the tools to create sustainable urban environments.

Cluster 4 centers on green sustainability, negative impacts of urbanization, and urban-development dynamics, containing 29 terms. Key terms like “green space”, “negative impact”, and “urban sustainability” illustrate the environmental consequences of rapid urbanization. This cluster draws attention to the role of green infrastructure in mitigating the adverse effects of urban growth and fostering ecological resilience. It aligns closely with global sustainability objectives, such as the United Nations’ Sustainable Development Goals (SDGs), particularly SDG 11, which focuses on sustainable cities and communities. The cluster reflects the growing emphasis on balancing urban development with environmental preservation.

Cluster 5, containing 27 terms, highlights using urban-quality indices, multi-criteria decision-making (MCDM) methods, and indices such as NDVI, MNDWI, and NDBI. Terms like “urban quality”, “NDVI”, and “decision maker” dominate this cluster, showcasing the importance of integrating various indicators to provide a holistic assessment of urban ecological quality. This focus on multi-dimensional evaluation methods underscores the necessity of considering ecological, social, and economic dimensions when planning for sustainable urban growth.

The interconnected nature of the clusters reveals several emerging trends and thematic overlaps, demonstrating the increasingly integrative approaches adopted in urban ecological-quality research. One notable trend is the blending of remote-sensing technologies (Cluster 3) with ecological indicators and analytical tools (Cluster 1), emphasizing the enhanced capabilities of spatial and spectral data in assessing ecological conditions. This integration allows for developing more nuanced urban-quality indices that can account for temporal and spatial variability, improving the accuracy and relevance of urban ecological assessments.

Another emerging trend is the synergy between spatial data analysis (Cluster 2) and sustainability-focused frameworks (Cluster 4). The growing emphasis on green infrastructure, reflected in Cluster 4, aligns with advancements in cartographic modeling and mapping techniques in Cluster 2. Together, these clusters highlight the increasing role of spatial technologies in promoting urban resilience through informed decision-making. Integrating spatial data with urban planning processes enables the identification of hotspots of ecological degradation and areas where green interventions can have the most significant impact.

The thematic overlaps between Clusters 4 and 5 reveal the field’s evolution toward incorporating multi-criteria approaches for decision-making. Advanced vegetation and land-cover indices, such as NDVI and MNDWI, are instrumental in evaluating the ecological health of urban environments. This trend signifies a shift from single-dimensional assessments to multi-dimensional frameworks that consider the interplay of ecological, economic, and social factors in urban sustainability.

The network also highlights the increasing role of policy-oriented research in bridging scientific findings and practical applications. Clusters 3 and 5 demonstrate integrating remote-sensing technologies and quality indices with policy-making frameworks. This trend underscores the importance of evidence-based approaches in designing policies that address urban ecological challenges.

Emerging research areas include exploring machine learning techniques and their applications in urban ecological studies, as hinted by terms such as “machine learning” and “algorithm” in smaller clusters. Additionally, terms related to “interactive coupling mechanism” and “spatial heterogeneity” suggest a growing interest in understanding the complex interactions between urbanization and ecological systems. These trends point to a future where urban ecological-quality research leverages cutting-edge technologies and interdisciplinary collaboration to address the multifaceted challenges posed by rapid urbanization.

3.3. Countries’ Collaboration

The global research landscape regarding urban ecological quality is predominantly shaped by a few select countries, as evidenced by the collaborative network depicted in (Figure 4). This visualization highlights the depth and breadth of international partnerships among researchers and institutions in this scientific field.

China stands out as the foremost contributor, responsible for a significant 33.3% of the overall scientific output. The United States and Iceland trail closely behind, each accounting for a substantial 16.67% share of the research. The top five countries also include France, Iceland, and Romania, each contributing 11.11%, while Australia maintains 5.56% of the total.

The varying thickness of the interconnected lines in the network graphic emphasizes the diverse and strong collaborative efforts that define research in the urban ecological-quality domain. This visual representation underscores the substantial involvement in joint research and knowledge exchange across national boundaries, thereby illustrating the proactive and globally collaborative nature of this scholarly endeavor.

The network depicted in (Figure 4), illustrates the extensive reach and interconnectedness of global urban-ecological quality research. International research partnerships facilitate the exchange of ideas, resources, and expertise, enriching the scholarly domain with diverse perspectives and knowledge.

The analysis indicates that a select group of nations are at the forefront of research efforts, with the top five countries contributing 83.33% of the collaborative work. China and the United States are the most prominent contributors, driving half of the global partnerships. This unequal distribution underscores the influential role of certain countries in shaping the research agenda and enabling worldwide knowledge exchange. Despite this concentration, the varying thickness of the connecting lines in the network visualization underscores these collaborations’ robust and multi-dimensional nature. The collaborative landscape mirrors the transnational essence of urban ecological-quality research as scholars and institutions from diverse backgrounds join forces to address this complex and globally significant field of study.

3.4. Influential Journals

The analysis in Figure 5 offers a comprehensive overview of the distribution of publications on urban ecological-quality research, across various journals. It reveals that 35 journals have actively contributed to the knowledge in this field, with the top 10 journals playing a significant role. Notably, Remote Sensing stands out as the leader, with an impressive four articles, accounting for approximately 9.09% of all publications (Figure 5).

Among the publications, the journal Sustainability stands out, with three articles accounting for approximately 6.82% of the total output. Following closely behind, Annales Universitatis Maria, Ecological Indicators, International Journal of Remote Sensing, and Journal of Ecology and Rural Environment each have two articles, collectively comprising around 4.55% of the total. Additionally, individual papers, representing roughly 2.27% each, were published in Applied Geography, Journal of Beijing Forestry University, the Canadian Journal of Urban Research, and the Chinese Journal of Applied Ecology.

3.5. Highly Cited Publications

A closer examination of the top 10 most-cited papers reveals that these publications account for a remarkable 79% of all references, accumulating an impressive total of 1354 citations, as illustrated in Figure 6. This highlights the outsized influence that a small fraction of academic literature exerts within the field, commanding significant attention and impact. Such a concentration raises important considerations regarding potential biases and prevailing trends in research. Further analysis underscores the pivotal role of these highly cited works in shaping the direction of research and the collective knowledge base within the domain (Figure 6).

Examining the most influential publications in the field reveals a strong emphasis on recent research, with a notable concentration of highly cited papers from the 2010s and 2020s. The top 10 most-cited articles represent a significant 49% of the total citations, with the highest coming from 2018, 2013, 2019, and 2020 at 361, 358, 68, and 41, respectively. In contrast, the 1990s, which had the highest total contributions within the top 10, only accounted for a mere 3.7% of the overall citations. This focus on contemporary research underscores the rapid evolution and ongoing shifts in the critical areas of interest within urban ecological quality (Figure 6).

3.6. Most Relevant Authors

The analysis of the top 10 most-prolific authors in urban ecological-quality research highlights their significant contributions in terms of publication volume and temporal patterns. This group, identified from a total of 156 unique contributors, represents the most active researchers in the field. On average, each paper involved 4.14 authors, although a few were sole-authored.

Notably, Xu H. and Zhang X. lead the list, with three published papers each, collectively accounting for approximately 7% of the total publications. Additionally, Bahi H., Cheng J., Geng J. and Hu X. emerge as other key contributors, each with two papers, representing around 4.4% of the dataset.

Beyond publication volume, this analysis also considers the number of citations per paper, providing a deeper understanding of the impact and influence of each author’s work over time (Figure 7). This dual focus on productivity and citation metrics underscores the pivotal role of these authors in advancing research within the field.

The analysis of the temporal publishing patterns of the leading researchers in the field of urban ecological-quality research indicates an inconsistent trend. Rather than demonstrating a steady, sustained output over time, the evidence suggests a more erratic and variable level of productivity, particularly prior to the 2020s. As depicted in Figure 7, the most prolific authors in this domain do not appear to have concentrated their highest publication volumes in specific years. Instead, their scholarly outputs fluctuate, without a clear, continuous pattern of productivity. This suggests that engagement and interest in urban ecological-quality research may be a more recent phenomenon, instead of reflecting longstanding, consistent contributions to the field across the 1990s-to-2020s period.

3.7. Trends in Most-Influential Publication

The review of the 34 selected papers reveals a strong emphasis on using remote-sensing technology to analyze patterns related to urban ecological quality. This reliance on remote-sensing approaches has been evident since the initial studies conducted in the 1990s (Table S1). Around 77% of the studies focused on cities, provinces, or regions in China, reflecting a regional bias towards studying urban ecological quality in the Chinese context (Table S1). This geographical focus suggests that researchers in China have been at the forefront of utilizing remote-sensing techniques to evaluate urban ecological conditions, potentially due to the rapid urbanization and environmental challenges many Chinese cities face (Table S1). This trend is also influenced by China’s policy initiatives, such as the Five-Year Plans, which emphasize sustainable urban development and ecological restoration, providing a policy-driven impetus for research growth. Furthermore, advancements in remote-sensing technologies during this period, including the widespread availability of satellite-derived data, played a pivotal role in shaping the research trajectory.

In contrast, the remaining studies were more geographically diverse, encompassing locations such as Canada, India, the United States, Iran, France, and Africa, suggesting the growing global interest in understanding urban ecological dynamics and the applicability of remote-sensing methods in diverse urban settings (Table S1). The least-represented subset of studies involved multiple locations, including South Africa, China, Chile, Australia, and Germany, or a broader geographical scope, covering several countries. This limited representation indicates the need for more cross-country comparative analyses to understand urban ecological quality better and the transferability of remote-sensing-based approaches across different national and regional contexts (Table S1).

The Remote-Sensing Ecological Index (RSEI) has emerged as a foundational tool for evaluating urban ecological quality, reflecting its widespread adoption and utility within the field. However, recent analysis reveals a dynamic evolution in the scientific field, with the emergence of a diverse array of advanced derivatives of the RSEI, including the Urban Remote-Sensing Ecological Index, Urban Quality of Life, Multisource Remote-Sensing EEQ Index, Urban Ecological-Quality Index, Eco-environmental Quality, Coupling Coordination Degree, Urban Quality-of-Life Assessment, Remote-Sensing Ecological Index with Local Adaptability, Urban Sustainability Index, Modified Remote-Sensing Ecological Index, and Eco-environment Index (Table S1). These derivatives illustrate the technological advancements driving research and the influence of evolving field trends and policy shifts. For example, the development of indices like the Urban Sustainability Index aligns closely with global sustainability initiatives such as the United Nations Sustainable Development Goals, which have encouraged more integrative and context-specific approaches to urban ecological assessments.

While these advanced indices are noteworthy, it is essential to acknowledge that less commonly used indices, such as Urban Ecological Quality, Urban Quality-of-Life Index, Ecosystem Service Value, Production-Living Ecological Space, Ecological Service Function, and Ecological Values, adopt a broader perspective by integrating diverse ecological, social, and economic indicators (Table S1). These indices reflect the field’s response to the growing recognition of urban systems as complex socio-ecological entities. This trend is further supported by global policy frameworks and the increased availability of high-resolution socio-economic and ecological datasets, facilitating more comprehensive evaluations. By integrating such diverse indicators, these indices help researchers and policymakers better understand the intricate interconnections between urban systems and their environmental impacts, supporting more informed decision-making and targeted interventions for sustainable urban development. This potential impact of the research underscores the importance and relevance of the ongoing work in this field (Table S1).

Upon reviewing the key indicators commonly employed in these indices, it is evident that the indicators directly derived from the RSEI remain the most widely used and fundamental components. These indicators, including the Normalized Difference Vegetation Index (NDVI), Normalized Difference Built-up Index (NDBI), Land-Surface Temperature (LST), and Land-Surface Moisture (LSM), are predominant (Table S1). Other less frequently used indicators, characterized by more complex structures, consider a wide range of factors, encompassing land use and cover, air quality, socio-economic and cultural data, and remote-sensing-derived information (Table S1). Including such diverse indicators reflects the expanding technological capabilities and the increasing emphasis on addressing the multifaceted nature of urban ecological quality.

The emergence of more advanced and comprehensive indices underscores the ongoing efforts to enhance and broaden the tools available for evaluating urban ecological quality. These efforts are driven not only by technological advancements, but also by dynamic policy shifts and the growing demand for interdisciplinary approaches. The field’s maturation reflects the recognition of the necessity for context-specific and holistic approaches to urban ecological assessments, which incorporate the diverse and evolving aspects of urban environmental dynamics (Table S1).

4. Discussion

The bibliographic analysis reveals critical insights into the evolution of research on urban ecological quality (UEQ) over the past three decades. A significant rise in publications, especially during the 2010s and 2020s, reflects the increasing recognition of UEQ as a vital area of study. This growth aligns with technological advancements, particularly in computational methods and remote-sensing technologies, which have greatly enhanced the analysis and interpretation of urban ecological data [48,90].

The findings are rooted in a conceptual framework centered on UEQ and the application of remote-sensing techniques. This framework leverages established methodologies, such as the Remote-Sensing Ecological Index (RSEI) and other satellite-derived indicators, to evaluate urban ecological conditions. Studies by Yang et al. (2023) [91] and Zhang et al. (2023) [92] validate the use of remote sensing to monitor spatial and temporal variations in ecological quality. Additionally, Lin et al. (2022) [93] demonstrate the integration of RSEI with the LandTrendr algorithm, enabling effective tracking of ecological changes in rapidly evolving urban environments.

A comparative analysis explores key drivers of UEQ, including land-use patterns, population density, and impervious-surface extent. Findings align with Huang et al. (2022) [94] and Ning et al. (2023) [95]. These studies highlight the negative impacts of impervious surfaces and high population density on ecological performance. Additionally, Lin et al. (2022) [93] and Xiang et al. (2022) [96] emphasize the temporal evolution of urbanization’s effects on ecological quality, underscoring the need for integrated urban planning to mitigate adverse outcomes.

Moreover, integrating remote-sensing data with sustainability-oriented indicators ties the findings to global sustainability goals. The observed positive relationship between economic development and ecological-quality improvement in specific urban contexts is consistent with findings from [97] and Xu et al. (2022) [98]. Notably, the coupling coordination degree model employed by Xu et al. (2022) [98] demonstrates the value of integrating urban planning with ecological preservation to promote sustainable urban development.

This study’s methodological contributions lie in using remote-sensing-derived indices as comprehensive tools for assessing UEQ. Techniques such as entropy-based weighting and high-resolution spatiotemporal analyses improve the precision and reliability of assessments. Studies by Huang et al. (2022) [94] and Lin et al. (2022) [93] provide robust evidence supporting the effectiveness of these methods. This alignment with broader trends validates remote sensing as a critical tool for monitoring urban ecological systems.

The observed surge in research activity, reflected in the increased publication output, highlights UEQ as a focal point for scientific inquiry. While the 1990s and 2000s saw modest publication rates, averaging 0.3 and 0.4 papers per year, the field experienced a notable upturn in the 2010s, with an annual average of 1.5 papers (standard deviation of 2.27). This trend accelerated into the 2020s, with six papers published annually on average (standard deviation 3.36), signaling the maturation and expansion of UEQ research.

A growth rate of 8.33% from 1997 to 2023 further emphasizes the increasing interest and investment in UEQ research. This growth reflects rising publication output and highlights the field’s importance in global sustainability efforts. Peak research years, such as 2023, 2021, and 2019, coincide with heightened policy attention to urban ecological challenges, demonstrating the responsiveness of research activity to societal needs [99,100].

The clustering of high-publication years around these dates suggests that the field is responding to both technological advancements and changing policy priorities, which are likely driving the increase in research activity. Moreover, the findings indicate that interdisciplinary approaches, integrating ecological, social, and economic perspectives, are becoming increasingly critical for effectively addressing the complex challenges posed by urbanization [101,102]. This integrative framework enables researchers to formulate more holistic strategies for improving urban ecological quality, thereby contributing to the overall sustainability and resilience of urban environments in the face of continued growth and environmental change [102,103,104,105].

Remote-sensing studies have shown that policies targeting ecological preservation and runoff mitigation significantly influence urban ecological quality (UEQ). High-resolution data capture the effects of green-space expansion and afforestation policies, which improve landscape patterns and mitigate the negative impacts of urban expansion on ecological conditions, as demonstrated by Huang et al. (2022) [94] and Lin et al. (2022) [93]. These findings highlight the role of remote sensing in assessing policy-driven changes in land use and vegetation cover.

Remote sensing also evaluates the impacts of impervious-surface reduction and watershed-conservation policies on runoff processes and ecological systems. By integrating hydrological models with remote-sensing data, studies such as Ning et al. (2023) [95] provide actionable insights into improving soil moisture and stabilizing runoff patterns, enhancing ecological resilience. This underscores the utility of remote sensing, combined with policy-evaluation frameworks, in managing the interactions between urban landscapes, hydrological dynamics, and ecological quality.

In addition to the growth in publication volume, the data also indicate a concurrent increase in the number of contributing authors, particularly in the recent decade. Between 2020 and 2023, the number of active authors reached a peak of 102, a substantial rise from the 47 authors during the preceding 2010–2019 period. This escalation in collaborative efforts is further evidenced by the increase in co-authorships per paper, which averaged 3.47 in the 2010s and 4.0 in the 2020s. The emerging trend of international co-authorships during the 2020s, the highest in the study period, suggests the development of an increasingly interconnected global research network. This global-scale collaboration reflects the complex and multifaceted nature of urban ecological-quality challenges, which necessitate diverse perspectives and expertise from multiple disciplines and geographical contexts [106].

The co-occurrence network analysis offers a detailed overview of the thematic and methodological diversity within urban ecological-quality research, illuminating the field’s evolution and increasing interdisciplinarity. This network consists of 190 distinct elements organized into six clusters, encapsulating the major research themes and approaches shaping the discipline. The central and largest cluster highlights the significance of methodological advancements, ecological indicators, and remote-sensing technologies, which have emerged as essential tools for assessing and monitoring urban environments. This cluster highlights essential methodological frameworks, including the Remote-Sensing Ecological Index (RSEI) development and the application of Principal Component Analysis (PCA). These methods are crucial for conducting thorough and scalable ecological assessments. They play a key role in standardizing ecological evaluations and improving the accuracy of spatial analyses.

The network analysis reveals a geographic concentration of research contributions, with China as the leading contributor (33.3%), followed by the United States and Iceland (16.67% each). The top five nations account for 83.33% of the field’s scientific output, highlighting the global, yet regionally concentrated, nature of the research. This distribution underscores the need for enhanced international collaboration to address urban ecological challenges globally.

The temporal clustering of high-publication years suggests that research activity is influenced by technological advancements and evolving policy priorities. The integration of remote-sensing technologies and advanced ecological indicators, such as the Normalized-Difference Vegetation Index and Modified Normalized-Difference Water Index, exemplifies how technological innovation drives methodological progress. These advancements are particularly evident in Clusters 3 and 5, which bridge the gap between theoretical research and actionable urban-management strategies by supporting multi-dimensional ecological assessments and urban-sustainability planning.

Clusters 2 and 4 highlight the integration of green infrastructure and spatial data analysis, demonstrating the critical role of spatial technologies in identifying ecological-degradation hotspots and optimizing urban planning. These insights reflect the increasing reliance on interdisciplinary approaches that combine ecological, social, and economic perspectives to address the challenges of rapid urbanization. Integrative frameworks enable researchers to develop holistic strategies for improving urban ecological quality and enhancing the sustainability and resilience of urban environments.

The co-occurrence network analysis maps the thematic and methodological evolution of urban ecological-quality research, underscoring the field’s trajectory toward greater interdisciplinarity and international collaboration. By integrating cutting-edge technologies and diverse research perspectives, the field can provide actionable insights for sustainable urban development and effective environmental management in the face of ongoing global challenges.

China is at the forefront of urban ecological-quality research, accounting for 77% of studies in this field. This concentration can be attributed to the country’s distinctive patterns of urbanization and pressing environmental challenges, including pollution and ecological degradation. The collaborative network within this discipline demonstrates robust international partnerships, crucial for tackling global urban ecological issues. As a result of rapid urbanization, China has made substantial investments in research, bolstered by advancements in remote-sensing technology and tools such as the Remote-Sensing Ecological Index (RSEI). Additionally, government initiatives that promote ecological civilization and sustainable urban development have further enhanced research output, underscoring the significance of data-driven urban planning and policymaking.

However, this geographic presence in urban ecological-quality research highlights the under-representation of Africa and Latin America, despite their significant challenges related to urbanization. It underscores the necessity for increased research funding, enhanced access to remote-sensing technologies, and greater global collaboration in these regions. To address this imbalance, the text advocates for capacity building, establishing international research partnerships, and developing region-specific ecological indices. Integrating diverse findings is essential for improving the global understanding of urban ecological dynamics and formulating inclusive strategies for sustainable urban development. Expanding research efforts beyond the dominant contributors is vital for capturing the complexity of these issues.

The fact that a select group of countries is driving most research efforts highlights the influential role of these nations in shaping the research agenda and fostering global knowledge exchange. The analysis of publication distribution across various journals reveals that 35 journals have actively contributed to the field of urban ecological quality, with the top 10 journals playing a particularly significant role. Remote Sensing emerges as the leading journal, accounting for 9.09% of all publications. Other prominent journals include Sustainability, Annales Universitatis Mariae Curie-Skłodowska, Ecological Indicators, International Journal of Remote Sensing, and Journal of Ecology and Rural Environment.

These journals collectively contribute to a substantial portion of the research output, reflecting their importance as platforms for disseminating knowledge in this field. The concentration of highly cited publications within a small portion of the literature suggests the presence of influential works that have shaped the trajectory of urban ecological-quality research. The top 10 most-cited articles account for 49% of the total citations, and these impactful papers were published between 2018 and 2020.

This emphasis on recent research highlights the rapid evolution of the field and the growing significance of contemporary studies in advancing our understanding of urban ecological quality. Furthermore, the analysis of key indicators and indices used in urban ecological quality research reveals a strong reliance on remote-sensing technologies and the Remote-Sensing Ecological Index as a foundational tool [42,103,104,105]. However, the emergence of more advanced indices, such as the Urban Quality-of-Life Index, Eco-environmental Quality Index, and Urban Sustainability Index, reflects the field’s maturation and the ongoing efforts to develop more comprehensive and context-specific approaches. These newer indices incorporate a broader range of indicators, including socio-economic, cultural, and environmental factors, which are crucial for capturing the multifaceted nature of urban ecological quality.

The text discusses the maturation of urban ecological quality, highlighting increased publication output, researcher collaboration, and diversification of themes and methodologies. It emphasizes the importance of this field in addressing environmental challenges related to urbanization. The study employs a comprehensive methodology combining traditional bibliometric analysis with systematic review techniques to identify trends and influential publications. Tools like Bibliometrix and VOSviewer are used for detailed data analysis and visualization, ensuring reliability and accuracy through rigorous screening and data integrity checks.

The text highlights key limitations of the methodology used in data analysis. These include the potential exclusion of significant terms due to a minimum-occurrence threshold of two in co-occurrence network construction, and the narrowing of focus by excluding gray literature, review articles, and conference proceedings, which may overlook valuable insights. Additionally, it notes that the binary counting algorithm in VOSviewer does not capture the nuanced relationships between concepts that more advanced text-mining algorithms could reveal.

The small sample size of 44 key publications may limit the findings, as it may not adequately represent the research field’s diversity and complexity. This reduced variability can lead to overemphasizing dominant themes and under-representing emerging research areas. It also hinders the detection of subtle trends, especially in less-studied contexts. Future studies should include more databases or broader search queries to improve representativeness and robustness.

This study offers valuable insights into urban ecological quality through remote-sensing technologies and bibliometric analyses. However, it is important to recognize some methodological limitations that may impact the extent and depth of its conclusions. While remote-sensing data are adequate for capturing large-scale spatial and temporal patterns, their heavy reliance poses challenges in fully incorporating socio-economic factors crucial for a comprehensive understanding of urban ecological quality.

Remote-sensing indices like the Remote-Sensing Ecological Index (RSEI) help assess physical and environmental attributes like vegetation cover, impervious surfaces, and land-surface temperature. Nonetheless, they often overlook important socio-economic dimensions such as population dynamics, income disparities, cultural practices, and policy impacts, significantly influencing urban ecological outcomes. This lack of direct integration of socio-economic factors hinders the contextualizing of ecological findings within the broader socio-political frameworks of urban development.

Future research could address existing limitations by integrating remote-sensing data with socio-economic datasets, employing multi-criteria decision-making frameworks, and leveraging advanced machine-learning models to synthesize diverse data sources. These approaches would yield a more holistic understanding of urban ecological systems, promoting strategies that harmonize environmental preservation with social equity and economic development.

The dynamic evolution of research on urban ecological quality is significantly influenced by policy shifts, technological advancements, and emerging trends, all of which contribute to fluctuations in publication numbers, over time. To address critiques of surface-level analyses, this discussion identifies specific factors driving these changes. For instance, China’s rapid urbanization and environmental challenges have established it as a global leader in this research field. National policy frameworks, notably the Five-Year Plans, have explicitly prioritized sustainable urban development and ecological restoration, directly stimulating research initiatives. These policies have encouraged adopting and enhancing remote-sensing technologies to tackle urban environmental issues, demonstrating how policy can ignite academic progress.

Technological breakthroughs have also accelerated research activities. The widespread access to high-resolution satellite data and the development of advanced remote sensing indicators—such as the Normalized-Difference Vegetation Index (NDVI), Land-Surface Temperature (LST), and Land-Surface Moisture (LSM)—have transformed the methodological landscape of the field. These tools enable researchers to conduct more precise and scalable analyses, significantly improving their ability to monitor urban ecological dynamics comprehensively. The emergence of new indices, such as the Urban Remote-Sensing Ecological Index and the Urban Sustainability Index, illustrates the technological advancements driving methodological diversification and adaptation to specific contextual challenges.

Global frameworks such as the United Nations Sustainable Development Goals (SDGs) have also played a critical role in shaping research trends. By emphasizing the interconnectedness of ecological, social, and economic dimensions, the SDGs have encouraged interdisciplinary approaches and the integration of diverse indicators in urban ecological studies. This has led to the development of holistic indices that account for socio-economic and cultural factors, alongside traditional ecological metrics. For example, indices like Ecosystem Service Value and Production–Living–Ecological Space reflect an effort to capture the complexity of urban systems, aligning research with global sustainability priorities.

The observed clustering of high-publication years around key technological milestones and policy initiatives highlights the dynamic nature of this field. For example, the increased use of remote sensing in the late 1990s and early 2000s coincided with satellite imaging and data-processing technology advancements. Similarly, the recent surge in publications reflects a response to the growing global awareness of urban sustainability challenges and the corresponding demand for actionable strategies.

By integrating these elements, this analysis goes beyond a superficial examination of publication trends, providing a more nuanced understanding of the factors that influence the evolution of research. It emphasizes the importance of considering the dynamic interplay between policy, technology, and societal needs, to grasp the complexities that drive research priorities and methodology shifts within urban ecological-quality studies.

Despite certain limitations, the selected methodologies offer a solid foundation for this review, yielding valuable insights into urban ecological quality. To enhance the scope and reliability of future studies, researchers could explore incorporating multiple databases, employing more sophisticated text-mining techniques, and adopting broader inclusion criteria. These adjustments would address existing limitations and contribute to a more comprehensive understanding of the field.

5. Conclusions

The examination of urban ecological-quality research from 1997 to 2023 highlights the substantial progress made in this field in terms of the breadth of inquiry and the depth of methodological innovation. This period has witnessed a significant expansion in scholarly engagement, underscored by the identification of key publications and a marked surge in research activity during the 2010s and 2020s. These advancements reflect the increasing recognition of urban ecological quality as a critical domain for addressing rapid urbanization’s environmental and socio-economic challenges. The adoption and refinement of computational and remote-sensing technologies have driven this progress, providing researchers with sophisticated tools to analyze and interpret complex urban systems.

The annual growth rate in research output over the study period underscores the rising global priority of urban ecological quality in sustainable-development discourse. Notably, the increasing prevalence of international collaborations during the 2020s signals a shift toward a more interconnected and multidisciplinary research landscape. As revealed by co-occurrence network analyses, the thematic diversity and methodological evolution within the field further emphasize its maturation. Research has become increasingly organized around critical clusters, addressing key areas such as remote-sensing technologies, environmental monitoring, and urban sustainability.

Moreover, the influence of a select number of highly cited publications highlights the pivotal role of foundational tools like the Remote-Sensing Ecological Index and its derivatives. These indices have provided a standardized framework for evaluating urban ecological quality. In recent years, advanced indices integrating socio-economic, cultural, and environmental dimensions have enriched the field, enabling more comprehensive and nuanced assessments. These advancements underscore the dynamic and evolving nature of urban ecological-quality research and its growing relevance in shaping strategies for sustainable urban development.

This study highlights the significant advancements in urban ecological-quality (UEQ) research over the past three decades, emphasizing the importance of remote-sensing technologies and interdisciplinary approaches in addressing urbanization challenges. However, future studies should focus on integrating advanced methodologies and addressing existing gaps to strengthen the impact of the research. For instance, developing more comprehensive indicators, such as the Urban Quality-of-Life Index and Eco-environmental Quality Index, offers opportunities for deeper exploration of socio-economic, cultural, and environmental dimensions in urban ecological assessments. These advancements could significantly enhance our understanding of complex urban dynamics, contributing to more effective urban planning and sustainable-development strategies.

Looking to the future, several promising directions for urban ecological-quality research can be identified. These include expanding cross-regional and cross-country comparative studies, developing more advanced and comprehensive indices that integrate socio-economic, cultural, and ecological indicators, and strengthening global collaboration through increased international partnerships. Additionally, focusing on understudied regions, particularly in developing countries, integrating research findings into urban planning and policy-making processes, and exploring emerging technologies such as artificial intelligence and advanced remote-sensing techniques will be crucial for addressing the global challenges of urbanization.

Future research should also prioritize leveraging multi-source data, such as hydrological models, socio-economic indicators, and high-resolution remote sensing, to provide a more holistic perspective. Incorporating machine learning and artificial intelligence for pattern recognition and predictive modeling can further enhance the precision and applicability of UEQ assessments. These advancements, combined with policy-oriented research, could foster actionable insights, aligning urban development with global sustainability goals and addressing the multifaceted challenges posed by rapid urbanization. These future directions offer hope and inspiration for advancing urban ecological-quality research.