**Background:** With 76% of the global population living in cities and urbanization accelerating, understanding the relationship between urban environments and mental health is critical. While urban settings offer advantages such as proximity to jobs, education, and services, they also increase risks for psychological stress and mental disorders. Physical activity and social interactions are known to improve mental health in urban residents, and walkable neighborhoods and people-oriented designs are recommended. However, the authors argue that existing research provides only preliminary insights into how individuals react to specific environmental features (e.g., greenness, noise) and under what conditions these exposures lead to more physical activity, social interaction, and improved mental health. The term "person-place interactions" describes these reciprocal, time-varying associations, which prior studies have not adequately addressed due to methodological constraints.
**Methods:** This is a viewpoint paper that synthesizes existing literature and proposes methodological innovations. The authors review evidence from systematic reviews and meta-analyses on built environment and physical activity (e.g., 46 reviews on physical activity, with 83% supporting positive associations between walkability and physical activity; 36 longitudinal studies showing new walking/cycling/public transport infrastructure increases overall physical activity). They also review evidence on mental health impacts, citing an overview of 11 reviews that found insufficient and heterogeneous evidence with critically low methodological quality in 80% of included reviews, and a meta-narrative review of 38 intervention studies on urban green space and mental health. The authors critique the limitations of place-based approaches (e.g., census tracts, buffer zones, postal codes) which neglect that individuals move through multiple locations daily. They cite a scoping review finding that only 2% (10/412) of studies used activity spaces and only 2% (8/412) used multiple-point buffering, while nearly a third (118/412) used place-based approaches. A survey of 1003 Chinese adults showed significant differences between home-buffer and time-weighted activity-travel buffer exposures. The authors propose ambulatory assessment approaches combining accelerometry, GPS, physiological sensors (heart rate, electrodermal activity), and ecological momentary assessment (e-diary) to capture within-subject, time-varying associations. They specifically advocate for triggered assessments that initiate e-diaries when predefined conditions occur (e.g., outdoor activity detected via GPS and accelerometry), citing a study of 46 middle-aged adults where momentary affective states varied significantly by social interaction intensity and greenness.
**Key Results:** The paper does not present original empirical results but synthesizes existing findings. Key reported evidence includes: (1) 83% of reviews support positive associations between walkability and physical activity; (2) 63-70% of reviews support positive associations between access to recreational facilities, shops, services, parks/trails and physical activity; (3) new infrastructure for walking, cycling, and public transport increases overall physical activity; (4) evidence for mental health effects of built environment is insufficient and heterogeneous, with 80% of included reviews having critically low methodological quality; (5) strong evidence exists for park-based and greenway/trail interventions promoting health and well-being through increased park use and physical activity; (6) a study combining black carbon sensors, galvanic skin response, and GPS found that increases in black carbon are related to higher stress responses during active travel, while green space and good active travel infrastructure are associated with lower stress responses; (7) a GEMA study found 72% of questionnaires were filled in at home rather than during outdoor behaviors, highlighting recall bias risks; (8) a triggered assessment study showed momentary affective states varied significantly due to different social and physical environments.
**Clinical Implications:** The authors argue that creating truly health-promoting urban environments requires moving beyond aggregate, place-based associations to understand person-place interactions at the individual level. This has direct implications for urban health policy: interventions such as adding cycling lanes may be ineffective if the fit between environmental features and target groups' needs, preferences, attitudes, and sociodemographic backgrounds is not considered. The proposed triggered ambulatory assessment approach could identify for whom and under which conditions specific environmental features improve mental health and increase physical activity. This would enable precision urban health interventions tailored to individual differences in lifestyle, psychosocial characteristics, and daily routines. The authors emphasize that interdisciplinary collaboration among spatial scientists, psychologists, sport scientists, computer scientists, and urban planners is essential to overcome methodological challenges in data processing, linking spatial exposures to individuals, statistical analysis, and ethical considerations around privacy and security.