Subscription information. BIA collects some general market info, as does Miller-Kaplan.
With Miller Kaplan you get a billing total for the market, as well as some breakdown as to local or national. You get (as a subscriber) your station or station group's rankings in the market, but no information about the other stations.
Interestingly, the CC cluster in our market (one of the 'departing markets') cut out Miller Kaplan this year. Probably because there were only three of us reporting, & it didn't take a PHD in math to figure out who was doing what--and that two of us were doing better than the Texas folks.