# Topology of the World Tourism Web
## 3 Results and Discussion
### Network Topology and Structure
#### 3.1.2 Countries' In-Degrees and Out-Degrees  
While each country could/should be interpreted, due to the limited space, only a few top countries will be discussed (while the interested reader can access the data for all countries in Supplementary Files S1 and S2). Figure 2 shows the in-degree distribution over countries, where the darker color of a country denotes a higher in-degree. For instance, the highest in-degree occurs for Canada, followed by the United Arab Emirates (UAE), Belgium, Uganda, and the United States, while the lowest in-degrees are for Andorra, Saint Kitts and Nevis, Saint Vincent and the Grenadines, and Turks and Caicos Islands. Besides that, there are additional 47 nodes with an in-degree of 0. This happens because of the lack of data--some countries appear only as a source node. The in-degree lines out the tourism connectivity of a country in a sense that tourists arriving from other countries create tourism connections, where the number of source countries is equal to the target country's in-degree. Following that interpretation, because of tourism, Canada is connected to most of the countries in the network. As it attracts guests from most of the countries, it can be assumed that Canada's touristic offer is diverse and appeals to tourists with different socioeconomic backgrounds and preferences. The highest out-degree is for the United States, followed by Canada, the United Kingdom, France, and Germany (Figure 3). The lowest out-degrees belong to Sint Eustatius, Johnston Islands, and Midway Islands. The out-degree indicates to how many countries tourists travel, where the observed country is the source country. Like the in-degree, the out-degree points out to the connections to other countries realized by the tourist. However, it might also point out to preferences of the country residents, where a higher number of visited countries indicates a higher diversification of tourists' preferences. However, when applying weights, the situation changes. As weights represent the number of tourist arrivals, they can serve as an absolute measure of a country's attractiveness. The highest weighted in-degree occurs for China, followed by the United States, Spain, Hong Kong, and Italy (Figure 4). This means that China attracted most tourists in 2018 and has the highest share in inbound tourism measured by the number of tourists. According to [8], the top countries in the 2014 tourism network by the weighted in-degree were China, the United States, France, Spain, and Italy. The comparison of the two networks reveals a perturbation in the leading positions over the years, where Spain and Hong Kong improved their positions, Italy continues to hold its fifth rank, while France is not part of the top five countries in 2018. The highest weighted out-degree (Figure 5) is for China, followed by the United States, Germany, Hong Kong, and the United Kingdom (UK). In 2014, China was ranked fourth by the weighted out-degree ([8], 2014 ranking: Hong Kong, Germany, the United States, China, and the UK). Since China has loosened travel restrictions, it has actively taken a share in the tourism industry, and partly due to the number of its residents, it has been rapidly ascending to the top position in the world tourism network. The weighted degree forms the following top ordering: China, the United States, Hong Kong, Germany, and the UK. In comparison to previous research [8], from 2002 to 2014, there were a few changes in the core countries, except for the rise of Asian countries and their inclusion in the core. Figure 3: Out-degrees. Source: authors. Figure 2: In-degrees. Source: authors. In the tourism network context, the in- and out-degrees might also be related to the diplomatic relationships between the countries, as well as major touristic happenings, instabilities, and natural disasters.