> You can sleep outside on the ground in a big group any time you want. Most cities have hundreds of people who do that every day. I think any one of them would gladly trade it for an air conditioned room with a bed.
Most parks I know have rules against entering past dusk, enforced with ticketing. In NYC there are closed gates which would physically prevent you from entering many parks.
I've only been to NYC a couple times but I remember seeing a lot of homeless people. I'm sure that there are resources you could use to find out where the unsheltered homeless population in NYC sleeps, if it isn't in the parks.
Must be cooler there than on the ground.. Having lived through a few NYC summers, they can really be the worst. Not only it gets incredibly humid and hot, there's at least one serious rainstorm each week to drench you. I always found summer in NYC is much worse than winter.
Most parks I know have rules against entering past dusk, enforced with ticketing. In NYC there are closed gates which would physically prevent you from entering many parks.