Beyond technical metrics: Key indicators as boundary objects for assessing environmental injustice in green space access and urban heat exposure — A scoping review

Unequal access to urban green spaces (UGS) and intensified exposure to urban heat islands (UHI) constitute pressing environmental justice challenges with profound implications for public health, climate resilience, and social equity. Indicators, as measurable proxies of these inequities, have become pivotal not only for technical assessment but also for mediating communication between scientific, policy, and civic domains. Despite their widespread adoption, systematic knowledge of their methodological diversity, cross-scalar comparability, and differentiated policy functions across social hierarchies, spatial configurations, and ecological contexts remains fragmented. This scoping review addresses this gap by mapping and synthesizing indicators applied globally to evaluate UGS access and UHI exposure, with particular attention to regional asymmetries between the Global North and South. Following Arksey and O’Malley’s framework, enhanced by Joanna Briggs Institute guidance and reported according to PRISMA-ScR standards, the review analyzed 87 peer-reviewed empirical studies published between 2015 and 2025. Results reveal three primary categories of key indicators: accessibility metrics, thermal exposure measures, and composite vulnerability indices integrating socioeconomic and environmental variables. Accessibility metrics consistently demonstrate that marginalized and racialized populations experience structural exclusion from UGS. Thermal indicators document the concentration of heat burdens in disadvantaged neighborhoods. Composite metrics provide multidimensional assessments of vulnerability while also exposing epistemic and infrastructural asymmetries in data availability and methodological complexity between regions. Across categories, indicators operate as boundary objects, facilitating interdisciplinary collaboration, linking spatial analysis with justice-oriented governance agendas, and shaping how environmental inequities are recognized and prioritized in policy arenas. In practice, they support municipalities in targeting investments, designing equity-oriented adaptation strategies, and monitoring climate resilience outcomes. Future research should advance methodological pluralism, participatory co-production with affected communities, and context-sensitive cross-regional comparability to ensure that indicator-based assessments contribute to, rather than inadvertently standardize or obscure, equity-centered climate adaptation.