The EAS regs require a city to be more than 70 miles from a large or medium hub (as defined by the gov't.), with a few exceptions. 200 miles only applies if the subsidy exceeds $200 per passenger. The twist is that every city with service in 1978 is essentially elligible, even NYC or LA, if they ever were in danger of losing all service.
There is a list of cities and subsidies as of Feb, 2001 that includes the distance from a large/med hub at:
It is interesting to read. For example, Topeka just qualifies at 71 miles.