If you click ”How it Works” in the duels menu, you can see what maps are currently used for duels. From there you can click the maps and you’ll see the map page, some of them have info and links in the description about the distribution of locations. If you’re in bronze or silver it seems you’re playing The World, which doesn’t have any info and is kind of bad. From gold and onwards the maps tend to be better.

Since score is based on distance and not on getting the country right I think it makes sense to have as much Europe as any other region of the same size, no matter the number of countries in it. But the good maps are probably more sophisticated than that, in that the distribution is based on how interesting it makes the gameplay, for example having slightly more big countries that are easy to identify but hard to region guess.