Great question! Northwell has hospitals spread out throughout Long Island and the greater NYC area (Manhattan, Queens, Staten Island, Westchester). Our main teaching hospitals are North Shore (on Long Island), Long Island Jewish (in Queens) and Lennox Hill (In Manhattan). That being said there are at least a half dozen more large hospitals all throughout the island and NYC you can rotate at! Most people do a mix of NYC and Long Island, but you can choose to do most of your rotations at one hospital (pediatrics and psychiatry are at dedicated hospitals).
The med school building is on Long Island so most people choose to live on Long Island near the school for the first two years to have an easier commute. It's totally doable to commune from Manhattan to the school, but it takes time and time is precious in med school. Most people then move between second and third year to be close to the hospitals they're rotating at - Someone rotating primarily in Manhattan will move to Manhattan, someone rotating in Queens will move to Queens, etc.
Personally I live in NYC and love it, I have all the benefits of living in the city and I'm not too far from any of my hospitals. But really you can make nearly anything work if you have a particular area you want to live or do your rotations in!