Quantitative Evaluation of Spatial Openness of Built Environment Using Visual Impact Analysis

This paper presents a quantitative approach for evaluating spatial openness of built environment using visual impact analysis.Firstly,the impact of built environment on the human visual sense is divided into two-dimensional visual impact and three-dimensional visual impact.We expand on the concept of Yoshinobu Ashihara's D/H index for spatial openness and develop a visual impact analysis model combining two-dimensional and three-dimensional visual impact to calculate the spatial openness of built environment.Using GIS-based visibility analysis techniques, two quantitative indices,Visible Ratio and Average Visual Obstructive Distance, are proposed for measuring spatial openness quantitatively.The approach presented can be applied in urban design,in particular for quantitative evaluation of building shapes and spatial configurations related to open space.