Introduction
Urban public spaces are fundamental settings for social interaction, civic engagement, and the development of social capital. Beyond their physical functions, these spaces foster social trust, collective identity, and a sense of belonging by providing opportunities for everyday interaction among citizens. However, rapid urbanization, changing lifestyles, and the weakening of neighborhood ties have reduced social cohesion in many cities, making the improvement of public space quality an important strategy for strengthening social capital. Previous studies have confirmed the positive relationship between public space quality and social outcomes. Nevertheless, most have examined only selected dimensions of public space quality or limited indicators of social capital. Comprehensive studies that simultaneously investigate the multidimensional nature of both concepts remain limited, particularly in Iranian cities. Kermanshah, which has experienced significant physical, demographic, and socio-cultural changes in recent decades, provides an appropriate context for examining this relationship. Therefore, this study aims to investigate the impact of urban public space quality on citizens' social capital and to identify the relative importance of different quality dimensions through a comprehensive structural model.
Methodology
This applied research adopts a descriptive-analytical design with a quantitative approach. Data were collected through a structured questionnaire administered to 384 residents of Kermanshah, selected using Cochran's formula and convenience random sampling in highly frequented public spaces. Urban public space quality was measured through five dimensions: physical-spatial quality, accessibility and connectivity, functional-activity quality, social-perceptual quality, and identity-semantic quality. Social capital was assessed using five dimensions: social trust, social networks, social participation, social interactions, and sense of social belonging. The questionnaire's reliability and validity were confirmed using Cronbach's alpha, composite reliability, average variance extracted (AVE), and convergent and discriminant validity tests. Data were analyzed using Partial Least Squares Structural Equation Modeling (PLS-SEM) in SmartPLS, evaluating both the measurement and structural models through factor loadings, path coefficients, R² values, t-statistics, and goodness-of-fit indices.

Results and discussion
The findings indicate that urban public space quality has a positive and statistically significant effect on citizens' social capital. The coefficient of determination (R² = 0.796) shows that nearly 80% of the variance in social capital is explained by the combined dimensions of public space quality, demonstrating the strong explanatory power of the proposed model. Among the five dimensions, physical-spatial quality and identity-semantic quality exert the strongest influence on social capital (β = 0.212 each). This finding suggests that social capital depends not only on the physical characteristics of urban spaces but also on the meanings, cultural values, local identity, and collective memories associated with them. Attractive, well-maintained, and comfortable public spaces encourage citizens' presence and interaction, while identity-rich environments strengthen place attachment, trust, and social cohesion. The social-perceptual dimension ranks second (β = 0.194), highlighting the importance of perceived safety, vitality, and the presence of other users in encouraging continuous use of public spaces and facilitating social interaction. These everyday experiences enhance interpersonal trust and reinforce citizens' sense of belonging. The functional-activity dimension (β = 0.181) also has a significant positive effect. Public spaces that accommodate diverse recreational, cultural, social, and economic activities provide greater opportunities for communication and the expansion of social networks than single-function spaces. Although accessibility and connectivity demonstrate the smallest effect (β = 0.162), their influence remains statistically significant. Easy access and integration within the urban network encourage the use of public spaces; however, accessibility alone does not automatically generate social capital. Rather, the social, cultural, and experiential qualities of public spaces determine whether physical presence evolves into trust, participation, and stronger social relationships. Overall, the findings demonstrate that social capital is produced through the interaction of physical, functional, social, and symbolic dimensions of urban public spaces. Within the socio-cultural context of Kermanshah, the identity-semantic dimension is particularly influential, indicating that local identity and cultural meanings are as important as physical improvements in strengthening social cohesion. These findings support an integrated approach to urban planning that simultaneously enhances environmental quality, local identity, social vitality, and opportunities for interaction among different social groups.

Conclusion
The study confirms that the quality of urban public spaces is a major determinant of citizens' social capital, positively influencing social trust, participation, social networks, interactions, and sense of belonging. The high explanatory power of the structural model further demonstrates that improving public space quality is a fundamental strategy for promoting urban social development. The results identify physical-spatial quality and identity-semantic quality as the most influential dimensions, indicating that social capital depends not only on citizens' physical presence in public spaces but also on the quality of spatial experiences, place attachment, local identity, and the meanings associated with urban environments. From a practical perspective, strengthening social capital in Kermanshah requires an integrated planning approach that combines physical improvements with the preservation of cultural identity, enhancement of environmental quality and safety, promotion of diverse public activities, and active citizen participation in the design and management of public spaces. Such measures can foster stronger social interaction, reinforce collective responsibility, improve urban quality of life, and contribute to sustainable social development. In conclusion, urban public spaces should be regarded not merely as physical components of the city but as dynamic social and cultural environments where social capital is created and reinforced. The conceptual framework developed in this study also provides a useful basis for future research examining the relationship between urban environmental quality and social capital in other Iranian cities and comparable urban contexts.