Simple Map
As developer says, this is a simple map of the NYC subway system. It does what it sets out to do. No need for data and it is free.
If you are good at reading maps, this app is for you. I used it constantly on my trip to NYC in conjunction with Google Maps. Google Maps (uses cellular data) is good at suggesting a route and this app is good at giving an overview of all the lines and different options and transfers.
Sure, the app could be updated to allow zooming and a pop up legend.
KSS42 about
NYC Subway Map, v2.0