We've got one group of ambassadors for a neighborhood of about 10k people. It's the downtown entertainment district. There's talk about expanding to three groups in other dense, business, or higher crime areas. Each group is roughly 5.
That expansion would make a 4000:1 population to ambassador ratio. So New York would need 2000-2500 total, about 400 of those being supervisors who know the area well.
They need to be visible, lightly armed, and willing to talk and help; rather than confront and escalate.
It's true community policing. Walking around, not driving through.
It would be a hard model to do in NYC, or any large metro. It'd be great, but hard to implement.