Compact and green urban development-towards a framework to assess urban development for a high-density metropolis

This paper proposes a framework for measuring compactness and urban green accessibility in a high-density transit-oriented metropolis and uses Taipei City and its surrounding outskirts, New Taipei City, as a case to illustrate the measurement framework. Two indices, urban compactness index (UCI) and urban green accessibility index (UGAI), are developed to illustrate various aspects of a sustainable urban built environment, with UCI including density of residents and commercial activities, land use mix, street connectivity, access to center/subcenters, and access to transit stops, and UGAI measuring access to public urban green spaces. We found that while great spatial variations exist among different parts, our study area has a distinguished polycentric pattern of UCI index with three distinct clusters around the center and sub-centers illustrating higher index values in 2015. When compared to UCI, UGAI has a similar polycentric but more dispersed spatial pattern, as well as linear patterns along river corridors. We found that most areas of medium or high UCI values are located in areas of either plan-induced or plan-expanded development. UCI values in areas of plan-expanded development are generally higher than that of areas of plan-induced development. UCI and UGAI are spatially correlated to a certain extent. We found that most centers and one particular subcenter have high UCI and UGAI, moving towards both compactness and good green accessibility. Two subcenters with high UCI and low UGAI, i.e. Banqiao and Yonghe, call for planning to provide green spaces for residents living in these rising subcenters. UCI and UGAI can be applied and used to assess compact and green urban development of other cities and they are particularly useful to dense urban environment of large cities in Europe and Asia.