“…It can be obtained by looking at the infrastructure such as a railway, roads or postal road network (Bretagnolle & Franc, 2017;Derudder, Liu, Kunaka, & Roberts, 2014), by looking at the moves of vehicles such as ships (Ducruet, Cuyala, & El Hosni, 2018) or by looking at actual traffic, which covers both goods and people. Numerous studies have looked at flows of people to measure intercity relations at the regional, national or global scales, whether it is air passengers (Derudder & Witlox, 2005), train passengers (Berroir et al, 2017) or commuters (Nelson & Rae, 2016). Recently, flows of people have also been identified through geolocated posts of people on social media (Lenormand et al, 2015;Zhang, Derudder, Wang, Shen, & Witlox, 2016), which allows to overcome the national dimension of data collection, but is not necessarily without representative bias.…”