Admittedly this is just a guess, but might the Carson velodrome explain Orange County's dominance in this index? There's precious little overlap in the Venn dia

Admittedly this is just a guess, but might the Carson velodrome explain Orange County's dominance in this index? There's precious little overlap in the Venn diagram of people who race track bikes (on tracks) and people who ride track bikes because bike messengers ride track bikes.