Relative Variability in Streetscape Skeletons and Spatial Association: Application for Identifying Harmonious and Inharmonious Streetscape Skeletons in Tokyo

Whether or not a streetscape skeleton (defined as the 3D street space) is harmonious depends on the degree of difference between heights and setbacks of adjacent buildings, which is called the relative variability in the streetscape skeleton, but this has generally been overlooked. Because streetscape skeletons are ambiguous, evaluating whether or not they are harmonious is thus conceptually and technically challenging. This article, therefore, considers the relative variability in streetscape skeletons and their spatial associations and answers the following question: where are harmonious or inharmonious streetscape skeletons locally clustered? The relative variability in the streetscape skeletons in the districts of the Tokyo metropolitan region was computed, where building heights and setbacks are directly controlled through streetscape promotion district planning stipulated in the City Planning Act. The spatial association of the relative variability in streetscape skeletons was then visualized to identify where streetscape skeletons are harmonious and inharmonious. The results showed that although harmonious streetscape skeletons are spatially clustered inside the domain bounded by wider streets, such clusters are small and spatially scattered. We, therefore, concluded that the effectiveness of direct controls through streetscape-promoting district planning to maintain and create harmonious streetscape skeletons is spatially limited and thus insufficient.