Exploring the provision, efficiency and improvements of urban green spaces on accessibility at the metropolitan scale

Accurately assessing urban green space (UGS) accessibility and proposing effective and specific proposals for UGS provision improvement accordingly is vital to urban development. Taking the metropolitan of Shanghai, China as the study site, this study first assessed its UGS provision by improved multiple step floating catchment area methods and multiple indexes, including UGS accessibility, theoretical capacity, potential demand, and traffic supply. Second, it investigated the impacts on citywide UGS accessibility justice for each UGS by comparing Gini index differences of citywide UGS accessibility between the conditions when exist and non-exist for each UGS. Third, it used ternary plots to explore the influence mechanism of the factors of UGS theoretical capacity, potential demand, and traffic supply on accessibility, and introduced an RGB color triangle to spatially and simultaneously display the effects of these three factors on accessibility for each UGS in Shanghai. Fourth, it assessed and classified the UGS provision efficiency for accessibility according to the relationships among the theoretical capacity, potential demand, and traffic supply factors by 3D scatter plot. Fifth, it proposed specific types and priorities of requirement for UGS improvement according to its impact on citywide UGS accessibility justice and the effect of its theoretical capacity factor on UGS accessibility. The findings showed that UGS accessibility and its three factors in Shanghai were correlative and had a spatial clustering trend in central city areas. The majority of UGSs showed positive impact on citywide accessibility justice, which went up with the values of accessibility and the three factors. Most UGSs were dominated by theoretical capacity power. The UGS provision efficiency was relatively good for most UGSs, which had relatively well-matched conditions and demands. The improvement requirements for UGSs on accessibility investigated in this study will improve UGS provision.