Wiegandt, Claus-C., et al. “Determinants of Online Shopping – an Empirical Study in Six North Rhine-Westphalian City Regions”. Raumforschung Und Raumordnung | Spatial Research and Planning, vol. 76, no. 3, June 2018, pp. 247–265, https://doi.org/10.1007/s13147-018-0532-5.