Automatic measurement of building setbacks and streetscape widths and their spatial variability along streets and in plots: integration of streetscape skeletons and plot geometry

Abstract

Measuring building setbacks and heights along streets is important for evaluating the variability of streetscape skeletons, the 3D spaces of streets defined by the arrangement of surrounding buildings. Its evaluation requires computing the streetscape width, defined as the front road width of a building plus the setbacks of both sides of the front roads, the building heights and the ratio of the streetscape width to the building height, known as the streetscape width-to-height ratio. However, measuring building setbacks and streetscape widths with geographical information systems (GIS) workstations remains theoretically and technically challenging because conventional methods fail to define the ambiguous boundaries of streetscape skeletons. To address this issue, we developed a new method for defining and measuring building setbacks and streetscape widths automatically and in a consistent way. A new basic spatial unit was also developed for evaluating the variability in building setbacks, heights, streetscape widths and streetscape width-to-height ratios not only in plots focusing on classical urban morphologies but also along streets focusing on a pedestrian perspective. The method contributes practically to the measurement and evaluation of streetscape skeletons in a bottom-up way at fine intervals without the need for setting predetermined spatial units.

KEY POLICY HIGHLIGHTS

• Measuring building setbacks and heights along roads is important for evaluating the variability of streetscape skeletons.

• However, measuring these in an actual complex urban space without vagueness on a GIS workstation is difficult.

• We have developed a new method for defining and measuring building setbacks and streetscape widths automatically.

• A new basic spatial unit for evaluating streetscape skeletons is proposed focusing on the plot geometry and a pedestrian perspective.

• The method contributes to the evaluation of streetscapes in a bottom-up way at fine intervals without setting predetermined spatial units.

Keywords:

• Streetscape
• setback
• street width
• plot
• variability

Acknowledgments

The author is grateful to the editor and three anonymous referees for their extremely valuable comments and suggestions.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data and codes availability statement

The data and codes that support the findings of this study are available with the identifier at the following permanent link (https://doi.org/10.6084/m9.figshare.20103140.v1).

Notes

1 In the literature, ratio of the building height to the streetscape width is alternatively adopted (e.g. Araldi and Fusco 2019, Fleischmann et al. 2021).

2 The skeletons of road polygons extracted by utilising a QGIS toolbox (e.g. v.voronoi.skeleton) can be adopted as an alternative data source of road networks representing road centrelines. However, I was unable to extract the skeletons of road polygons in this way and thus, an alternative data source of road networks representing road centrelines was adopted.

3 These two types of ordinary Voronoi polygons can be identified by the following steps: (1) selecting a set of V(Q_i,k) on the vertices of building polygons {B_i}; (2) generating the buffer zones whose width is 0.1 m from the perimeter of AV(B_i); (3) erasing a set of V(Q_i,k) on the vertices of B_i by the buffer zones and {B_i}; (4) generating the buffer zones whose width is 0.05 m from the output in step 3; (5) selecting V(Q_i,k) on the output in step 4.

Additional information

Funding

This research was supported by the Japan Society for the Promotion of Science [20H02383 and 22H00245].

Notes on contributors

Hiroyuki Usui

Hiroyuki Usui received Ph.D. from the University of Tokyo in 2014 and now is an assistant professor at the Department of Urban Engineering at the University of Tokyo. His research interests are city planning, urban morphology and spatial analysis. He published papers in spatial analysis-related journals, such as the International Journal of Geographical Information Science, Environment and Planning B: Urban Analytics and City Science and Computers, Environment and Urban Systems.