It seems pretty off, though. For example, the page for Iceland says that winter is the peak time, but it's actually pretty dead in the winter with the peak in the summer. Seems like people start planning their summer trips around December (plane tickets for Christmas?). Other places seem shifted up a month or two - the page for Paris has the peak season around May-June, but it's actually more like June-August.
OP, if you want to improve this, could you get some actual tourist data and experiment a bit with which other metrics (various Google searches - something like taxi services might be more accurate to estimate how many people are actually traveling in the country at the time, hotel prices, plane ticket prices, etc) best predict the tourist numbers?
OP, if you want to improve this, could you get some actual tourist data and experiment a bit with which other metrics (various Google searches - something like taxi services might be more accurate to estimate how many people are actually traveling in the country at the time, hotel prices, plane ticket prices, etc) best predict the tourist numbers?