I came across two maps today that seem to suggest that Californians are the athletic giants of the United States. Business Insider created this map of the gold medals won by athletes from each state in all the modern Olympic games (since 1924).
The States With The Most Olympic Gold Medals map, at first glance, appears to prove that "California is the most athletic state in the country". This is backed up by this map of college football players from Mode.
Where Football Players Call Home map visualize where college football players come from. The map certainly shows that a lot of college footballers come from California.
However both these maps are good examples of why you should normalize for population when creating these kind of heatmaps. California is the most populous state in the USA. Therefore if we create any kind of heatmap, whether for crime, the most millionaires or the most people living in poverty, if we don't normalize for population density then we would expect California to rate fairly highly - simply because it has the most people.
Actually the Where Football Players Come From map does allow us to view a 'per capita' map. Here's the map for the number of college footballers from each state after the data is normalized for population.