dojos.info just introduced the concept of Dojo Density. This is a measure of population vs number of Martial Arts Schools listed in a given place. At the moment, Dojo Density is available at dojos.info/USA/ for each state in the USA. We are using the 2014 Population estimate from the United States Census Bureau.
Here is an example chart showing every state and it's Dojo Density:
We are working on making this information available for all major metro areas, and how they compare with the national average. This should help you with better understanding the Martial Arts market.