1. Introduction
High-density urban areas are facing numerous challenges due to urbanization, such as environmental pollution [
1,
2], the urban heat island effect [
3,
4], and a growing disconnection between people and nature [
5]. A substantial body of research highlights that exposure to natural environments provides significant physical and mental health benefits for urban residents, including stress reduction, attention restoration, positive emotional states, and disease prevention [
6,
7,
8]. However, as urban density rises, per capita green space is decreasing, reducing access to nature in cities [
9,
10]. In this context, informal green spaces (IGSs) have garnered increased attention as potential solutions.
IGS refers to urban green spaces that are not formally planned and are characterized by spontaneous vegetation and irregular maintenance [
11]. Introduced by Rupprecht and Byrne, examples of IGSs include vacant lots, brownfields, and the edges of streets or railroads [
12]. Unlike formal green spaces, which are intentionally planned and maintained, IGSs tend to emerge in neglected urban areas, exhibiting a disorganized and heterogeneous appearance [
11,
13]. This natural disorganization, however, is exactly what grants IGSs unique ecological and social functions, supporting biodiversity and offering unstructured recreational opportunities [
14,
15,
16]. Furthermore, IGSs enhance ecological resilience in urban development by providing essential green infrastructure services, such as regulating temperature, pollution control, and disaster mitigation [
17,
18]
Research on IGS varies in focus across different regions globally. In Europe, especially in Poland, several studies have shown that IGSs contribute significantly to the well-being of urban residents and ecosystem services [
18,
19]. In addition, Sikorska et al. state that IGS has the potential to reduce inequitable distribution of urban green space availability [
15]. In Asian countries, particularly Japan and China, research on IGS has focused more on residents’ perceptions. In Japan, studies often use questionnaires to investigate residents’ views, usage patterns, and management preferences regarding IGS [
20,
21]. In contrast, Chinese researchers, such as Chen et al., have employed machine learning techniques to accurately measure and analyze residents’ complaints about IGS on social media platforms [
13]. Rupprecht et al. conducted two cross-cultural studies exploring residents’ perceptions of IGS in Australia and Japan, finding that the functional role of IGS in the lives of respondents from both countries was quite similar [
14,
22]. However, how the respondents used and evaluated IGS was closely tied to their personal environmental preferences.
Urban residents hold mixed attitudes toward IGS. Some residents prefer the less manicured, more natural appearance of IGSs compared to formal green spaces and already use IGSs for activities such as children’s play, dog walking, and barbecuing [
23]. Meanwhile, the unofficial and unmanaged nature of IGS raises safety concerns for others, limiting the full realization of its potential [
23,
24]. The lack of formal protection for IGS further limits its potential as a valuable urban resource [
25].
In densely populated urban environments where formal green spaces are limited, IGS can provide substantial social and environmental benefits, but its potential has not yet been fully realized [
20]. To unlock the potential of IGS in high-density urban areas, it is crucial to better understand the specific contributions that IGS can make to human well-being [
21]. Although most existing studies have focused on the spatial distribution [
25,
26], resident attitudes [
13,
14,
27], and ecological functions like biodiversity and climate regulation [
11,
19,
28], limited attention has been paid to its potential restorative effects on mental health. Herman et al., for instance, examined the emotional well-being of 20 participants using a portable electroencephalography device during their visits to IGS but found no significant difference in emotional states compared to visits to formal green space [
17].
To further investigate the mental health benefits of IGS, this study introduces Perceived Restorativeness as a key indicator for measuring the psychological benefits provided by urban green spaces [
29,
30]. According to Kaplan et al.’s Attention Restoration Theory (ART), perceived restorativeness refers to the extent of psychological recovery that an individual experiences in a given environment, typically linked to reduced mental fatigue, restored attention, and improved mood states [
31,
32]. Numerous studies have demonstrated that individuals perceive higher levels of restorativeness in natural environments compared to urban settings [
33,
34,
35,
36,
37]. Despite the potential for IGS to provide higher levels of perceived restorativeness due to its natural features, there is still a lack of empirical evidence to support this assumption [
38]. Most existing studies on restorative effects have focused on traditional green spaces (e.g., parks and gardens), often employing methods such as on-site questionnaires, photographs, or video assessments [
39,
40]. However, these methods have limitations when applied to IGS, as they are typically not designated by management authorities or owners for public use, and their disorganized and uncertain nature makes them less visible to the public [
25,
41]. Many people have little direct experience with IGSs, and relying solely on these methods may fail to accurately capture their restorative potential or could underestimate their contribution to psychological well-being [
21]. Considering this, this study aims to fill this research gap by validating the perceived restorative function of IGS through surveys of participants’ experiences following their on-site visits, while considering the specific characteristics of IGS environments.
One distinctive feature of IGS is the absence of designated pathways, meaning that individuals’ choices regarding route selection and the duration of their visit can significantly influence their green space experience, potentially leading to varying levels of psychological restoration [
42,
43]. Spatio-temporal behavioral patterns—referring to the trajectories and time-related dynamics of individuals’ movements across space—capture how people navigate environments and interact with different areas [
44]. GPS-based tracking systems provide an effective tool to capture such movement patterns, shedding light on how individuals explore and experience IGS over time [
45,
46]. This study introduces GPS-based spatio-temporal data to link movement patterns with perceived restorativeness, providing a dynamic approach to understanding the utilization of IGS.
Spatio-temporal analysis has been widely used in various fields to better understand movement patterns, space exploration behaviors, and visitor flows [
46], to analyze public space use [
47], and to monitor urban mobility [
48,
49]. In particular, spatio-temporal clustering techniques have been proven effective in identifying tourist characteristics and understanding how visitors use different spaces. For example, Liu et al. [
50] utilized open GPS trajectory data in mountainous scenic areas to identify microscopic movement patterns, revealing key insights for managing tourist flows and resource allocation. Brian et al. [
51] applied spatio-temporal analysis of GPS trajectory data to cluster and compare travel groups in a national park, helping optimize resource allocation and management strategies by identifying the time visitors spent in different areas. Research methods that employ GPS trajectory data to analyze visitor behavior within destinations have become relatively advanced [
52]. By treating IGSs, which are less restricted spaces, as small-scale destinations and combining spatio-temporal behavioral data with perceived restorativeness assessments, it is possible to provide a more precise and dynamic analytical perspective. This approach allows for a more nuanced understanding of how different route selection in IGS environments influence visitors’ restorative experiences, providing valuable insights into how these informal spaces can be better integrated into urban planning to enhance human well-being. Ultimately, this study will propose specific planning and management strategies for IGS based on the analysis results, aiming to better realize their potential as a valuable resource for enhancing the well-being of urban residents.
Although previous research has examined IGS across various urban contexts, there remains limited understanding of how visitor behaviors specifically influence their perception of restorativeness. This study seeks to bridge that gap by employing GPS-based spatio-temporal analysis in conjunction with psychological assessments of restorativeness, offering new insights into how different routes and behaviors within IGS impact mental well-being. The study aims to address the following key research questions:
- (1)
What are the spatio-temporal behavioral patterns of visitors within IGS?
- (2)
How do these behavioral patterns influence visitors’ perceived restorative effects?
- (3)
How can the findings from these patterns inform the planning and management of IGS to optimize their use and enhance restorative experiences?
Through this research, we aim to provide a scientific basis for the integration of IGS into urban planning, offering new insights and practical recommendations for the allocation of limited natural resources in high-density urban areas.
5. Conclusions
This study highlights the importance of integrating spatio-temporal behavior data with perceived restorativeness assessments to enhance the understanding of the restorative potential of informal green spaces. The findings demonstrate that both physical attributes (such as coverage area and path length) and psychological experiences (such as feelings of escape and fascination) play crucial roles in shaping visitor experiences and their perceptions of restorativeness. Our findings reveal that visitors’ engagement with IGS—characterized by varied spatial coverage, path length, and duration—significantly affects their perception of restorativeness through distinct behavioral patterns. These patterns operate through different dimensions of environmental experience, such as psychological escape, fascination, and exploration, offering critical insights for urban planners and landscape architects aiming to design IGSs that accommodate diverse user needs and enhance urban well-being.
From a planning and management perspective, the findings suggest that enhancing the spatial diversity, accessibility, and ecological features of IGSs can significantly improve their utilization and restorative potential. Preserving spatial diversity while adding minimal interventions, such as signage or clear pathways, could maintain the informal nature of these spaces while making them more navigable and appealing to a wider audience. Incorporating restorative elements like diverse vegetation, water features, and quiet spaces for relaxation could further enhance the psychological benefits of IGSs. Additionally, promoting public awareness and community involvement is essential for increasing engagement with these spaces. Targeted programs and community education can help improve the positive perception of IGSs, supporting their integration into urban environments as valuable resources for well-being.
Moreover, this study supports prior research on public attitudes toward IGSs, showing that while some individuals appreciate the unstructured nature of these spaces, others may have reservations about their safety or accessibility. This underlines the need for careful planning and management strategies to optimize IGS usage while maintaining their unique character. In particular, Visitor-Employed Photography (VEP) proved valuable in capturing authentic and reflective evaluations of IGSs, providing participants with the opportunity to engage with and assess these spaces in a more personal manner. This approach, while useful, also highlights potential biases, as it relies on subjective participant perspectives.
However, VEP, while effective in offering personal insights into participants’ experiences, also introduces potential subjective biases. Participants may focus on elements that align with their preferences or prior beliefs, leading to selective representation of the IGS environment. These subjective perceptions may not fully reflect the broader user experience, which could influence the findings related to restorativeness. Future research could mitigate this bias by incorporating more objective measures, such as physiological data (e.g., heart rate or EEG) or additional mixed methods to balance personal impressions with more quantitative assessments.
Additionally, the sample primarily consisted of students within a narrow age range, which limits the generalizability of the findings. Future studies should expand to include a broader demographic, encompassing various ages, occupations, and cultural backgrounds, to capture a more comprehensive spectrum of perceptions and behaviors. In addition, the influence of seasonal and temporal variations on IGS usage remains underexplored; understanding these patterns could be pivotal in optimizing green space design for year-round engagement and restorative benefits. Future longitudinal studies could investigate how IGSs are utilized year-round, capturing the temporal changes and seasonal fluctuations that may affect their restorative potential. Understanding these patterns will be pivotal in optimizing green space design for year-round engagement and psychological benefits. Investigating these aspects further will refine strategies and provide more nuanced guidelines for maximizing the restorative potential of IGS in diverse urban contexts. Building on this, cross-cultural studies can help explore how different populations in diverse urban environments engage with IGS, adding a comparative dimension to the research. This could reveal cultural differences in the perception of restorativeness, as well as how environmental factors like vegetation, pathways, or facilities are valued across regions. Long-term monitoring of IGSs could also capture how perceptions of restorativeness evolve over time, particularly in the context of urban development and ecological changes.
In summary, this study provides a basis for future research to optimize IGS design and management strategies that integrate visitor behavior patterns and restorativeness perceptions, aiming to enhance user engagement and maximize restorative experiences in urban environments.