This line graph shows the number of people who have visited a popular tourist destination over a period of time. It provides a visual representation of the number of visitors to the destination and can be used to identify trends in tourism.
From Wikipedia
In the mathematical discipline of graph theory, the line graph of an undirected graph G is another graph L(G) that represents the adjacencies between edges of G. L(G) is constructed in the following way: for each edge in G, make a vertex in L(G); for every two edges in G that have a vertex in common, make an edge between their corresponding vertices in L(G).