Supplementary Information Heterogeneous length of stay of hosts’ movements and spatial epidemic spread

Length of stay is a key factor in the management and development of the tourism industry and represents an important issue of debate for the economic literature [1, 2, 3]. Due to its importance for the economy, data on the average length of stay of travellers are collected by public and private agencies in several countries of the world, at different geographical resolutions. When considering official tourism statistics, it is important to point out that the statistical definition of tourism is broader than the common, everyday definition, because it encompasses not only private travel but also business travel. This is the case, for instance, of the definition of tourism given by Eurostat [4]. Similarly, tourism surveys of several countries cover a wide range of travel purposes, including holiday, but not limited to it: people travelling to visit relatives and friends, or for educational purposes, are also included in the statistics. This is primarily because the agencies view tourism from an economic perspective. Many of the statistical datasets are publicly available and can be downloaded from the internet. They usually provide the average length of stay of travellers in a defined country, along with the travellers’ country of origin, purpose of visit and local destination. Even if data do not provide information at the individual level, all the available statistical sources show that the length of stay of travellers around the world is broadly distributed, usually spanning several orders of magnitude in time. Moreover, the length of stay varies between different geographic locations within the same country. In the following subsections we list the main sources of our empirical findings, organized by reporting country.