Acknowledgements

We are grateful to the City of Wuppertal and Geobasis NRW for providing data. Map data copyrighted OpenStreetMap contributors and available from https://www.openstreetmap.org. We also wish to thank Paul Pflugradt, Jonas Kirstein and Rainer Wunderlich for their constructive comments on previous versions of this article as well as Tobias Loga for providing essential references. The authors would like to thank the Editors and anonymous Reviewers for their constructive comments that are greatly contributive to improving the manuscript.
This study is financially supported by the Ministry of Science and Technology, Taiwan, ROC (MOST: 107-2627-M-002-012, and 107-2621-M-002 -004 -MY3).