Fragmented but greener? Bad geography promotes higher green space accessibility: evidence from 356 Chinese cities

• Natural barriers are positively linked to green space access in most Chinese cities. • Smaller cities, despite more barriers, often have better green accessibility. • Vulnerable groups face longer walking times, especially in South and East China. • Economic strength enables cities to turn geographic barriers into green assets. • Higher education levels link to lower green access in South China cities. Access to urban green spaces is a critical element of sustainable and equitable cities. However, most existing studies have primarily focused on socioeconomic inequality in green space accessibility, while the role of natural geographic constraints—such as mountains and water bodies—in shaping accessibility remains underexplored. This study bridges this gap by providing a national-scale assessment of urban park accessibility across 356 Chinese cities, integrating both geographic and socioeconomic dimensions. Using high-resolution data on park locations, residential communities, and road networks, we estimate walking and driving accessibility to urban parks through a modified three-step floating catchment area (3SFCA) model. We then measure geographic constraints in two aspects: the proportion of barriers ( share of barriers ) and the complexity of their morphology ( nonconvexity ). The results reveal that natural barriers can enhance green space accessibility under certain conditions—higher nonconvexity is associated with shorter walking times to parks (β = –1.176, p < 0.001) and higher accessibility (β = 3.348, p < 0.1). However, these effects are uneven across cities: smaller cities generally perform better due to their compact urban forms, whereas mega cities experience longer travel distances and higher inequality. The interaction between geography and economic capacity is also significant, as wealthier cities are better able to mitigate geographic constraints through infrastructure and planning. This study provides new empirical evidence that geography fundamentally influences the equity of green space access, and offers new insights for developing sustainable urban design and policy strategies in topographically diverse regions.