Morphological, Historical, and Cultural Study on Gap between Buildings

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The purpose of this study is to propose a method of quantification of the gap between buildings, which is one of features in Japanese urban space, and to clarify the characteristics of area and distribution of these gaps.The gap was defined as an area where a circle of radius r cannot sweep through on a building location map. The diameter of the circle stands for the width of a gap. To extract the gap-area, operations in image-processing method called erosion and dilation were applied. That is, after digital imaging of a building location map, building planes were dilated in terms of a digital figure corresponding to a circle of r and then eroded. This procedure is equivalent to a closing operation in morphology and enabled the extracting gaps.The following results were obtained by applying this procedure to the whole building location of Tokyo 23 wards and Osaka 24 wards.1)In Tokyo, the gap ratios (gross area ratios) at three different widths of gap were 0.5% at l.5m width, 1.4% at 2.5m, and 2.4% at 3.5m. In Osaka, 0.6%, 1.3%, and 2.0% respectively. Locally, there were many areas with a ratio more than 10%, therefore the quantity of gap cannot be neglected in urban area.2)The gap ratios and index of density (building density, perimeter-ratio, building coverage) were highly correlated.3)High gap ratio areas are located circularly along the periphery of JR Yamanote line in Tokyo and along the periphery of JR Osaka Kanjo line. These areas overlap with densely built-up residential areas, that is, large population, low green coverage, and high earthquake risk areas, therefore problematic areas for safety.In this study, a little consideration was taken for historical and cultural processes of gap generation. Some functions of gaps were exemplified by a field survey.