Comparison of precise and approximated building height: Estimation from number of building storeys and spatial variations in the Tokyo metropolitan region

Abstract

Precise building height is indispensable for evaluating variability in building heights. However, relevant data are not always available. Conventionally, building height is approximated as the product of the number of building storeys and floor height, called approximated building height. However, there is no consensus on how floor height, a key determinant of approximated building height, should be set. In Japan, increasingly precise building height data are becoming available as an open 3D urban model. This provides the motivation for answering the following research questions, in the context of the Tokyo metropolitan region: (1) What is the difference between approximated and precise building height? (2) How should we set floor height to minimise the difference between approximated and precise building height? The results show that (1) the average difference is −3.46 m if floor height, c, is 5 m, −0.87 m if c is 4 m and 1.71 m if c is 3 m; (2) c = 4 can effectively estimate building height from the number of storeys; and (3) the greatest difference between approximated and precise building height is spatially clustered where commercial zones and industrial zones are allocated, with their degree being dependent on how floor height is set. Furthermore, it is found that (1) in commercial zones and industrial districts, the optimal floor height, defined as the optimal solution which minimises the sum of squared differences between approximated and precise building height, is greater than 4 m; (2) in mid/high rise residential districts, the optimal floor height ranges from 3 to 3.4 m; and (3) in low-rise residential districts, the optimal floor height ranges from 3.5 to 3.9 m. The findings of this paper can help urban planners find the optimal floor height in each district and understand spatial variations in building and floor heights.