Where athletes in professional sports come from

Sports are growing more international with respect to the athletes. Gregor Aisch, Kevin Quealy, and Rory Smith for The Upshot show by how much, with a focus on leagues in Europe and North America.

I like how: The dominant home country in each chart doubles as background and a layer; the tooltip shades the country you moused over while still showing the other countries; and the missing data and gaps are shown clearly but don’t obstruct the overall view.