This graph shows the number of Mario Kart players registered on MKLeaderboards by country.
I forgot to label the legend, so here it goes:
White: 1 to 3 players
Blue-white: 4 to 9 players
Blue-green: 10 to 29 players
Light green: 30 to 99 players
Green: 100+ players
I also find it interesting that every country in Africa has 1 player except for South Africa, which has 5 players.