# Topology of the World Tourism Web
## 2 Materials and Methods
### Definitions and Data  
The data from secondary sources are used, most of it from UN World Tourism Organization as they offer a most comprehensive database on the topic. The usual approach to SNA considers the use of a finite population with enumerated elements or the entire population, which is, in this case, all the countries. However, data availability and establishing the limits of the network are common problems in SNA [19]. We started from the list of countries by UN Arrivals of Non-Resident Tourists/Visitors, Departures and Tourism Expenditure (UN World Tourism Organization (UNWTO)), involving 221 countries. The literature conceptually differentiates travelers, visitors, and tourists. These conceptual differences also represent different measurement recommendations [9]. The data available at UNWTO are compiled according to [9], so their definitions are relevant to this research. A traveler is the person \"who moves between different geographic locations for any purpose and any duration\" [9]. A visitor is \"a traveler taking a trip to a main destination outside his/her usual environment, for less than a year, for any main purpose (business, leisure or other personal purpose) other than to be employed by a resident entity in the country or place visited\" [9]. Tourists are equal to overnight visitors (same-day visitors are excursionists, and travelers passing through the country are transit passengers), and tourism is a subset of travelers and visitors [9]. Overnight visitors or tourists usually require some type of accommodation, where they are subject to a survey or registration for which they provide personal information or characteristics of the trip. While such surveys do not primarily serve to determine the number of arrivals based on the country of origin, such data are often used instead of the border report if such report cannot be obtained. The country of residence can be differently classified by different forms of tourism and its recommended classification, but it must be determined by a question. The travelers' nationality is usually referenced in the passport, but it does not have to refer to the same country as the country of residence, as people might have more than one nationality and more than one passport [9]. However, when information about the country of residence cannot be obtained, the nationality data are used as a supplement. International Recommendations for Tourism Statistics (IRTS) 2008 [9] differentiates internal, national, and international tourism. We focused on international tourism, based on the number of arrivals of tourists by their country (other than the country where they have their residence). While obtaining available data, we learned how true a statement from [9] it that \"tourism is a phenomenon for which statistical representation has its particular challenges because of its special nature,\" as available reports reveal a variety of approaches and inconsistencies in reported data over the countries. Most of the countries report the number of arrivals at national borders. However, some of them report tourists by their country of residence, while others form the report based on the tourists' nationality--rarely both. Some countries do not check the duration of the travel at the borders and hence do not distinguish tourists from visitors, so they report all people entering as visitors. At the same time, countries that do distinguish tourists from visitors rarely report the number of visitors at the borders. In addition, some countries belong to zones in which national borders are abolished (for example, Schengen), where the movement of people is unrestricted. Due to impossibility of control at the borders, those countries usually report the number of arrivals based on the reports from accommodation units. There is also a distinction in reports regarding the use of all accommodation units or just hotels and similar establishments.