Just found this map of all 10-minute frequency or better services in New York City, by this not readily identifiable character on Tumblr. This looks like quite a struggle to make clear given the complex nomenclature that NYCTA uses.
The whole thing is here. An NYCTA contact tells me it's still current except for a change around LaGuardia airport.
When I'm learning a new city -- as I do 10 or 20 times a year as a consultant -- this is what I need!