I like to say that certain districts have borders. For instance, getting into the Redmond Barrens is a bit more of a process than just walking in. There's Touristville, which is easy access and (relatively) low-crime. But then there's the actual Barrens, which are sort of walled off against incursion by authorities. The cops don't go to the Barrens for a reason, and I see part of that reason as caused by the gangs. The gangs block off their territory when they have the manpower and resources to do so - they don't look for SINs, they just look for colors.
So the Barrens are like a war zone in my game - each of the gangs has their turf, colors, etc. and if the players aren't wise to the ever-shifting boundaries and such, they could get in deep drek.
Ironically, this isn't much different in a corporate enclave or high-security neighborhood. But instead of flaming cars and walls of tires and rebar, the neighborhoods have drones and gates. If someone's going into Bellevue, they need to be aware of the security in the area, especially the security that one cannot normally see. Cameras are everywhere, from the walls of buildings and fences to the drones in the skies. One might only see one police car on patrol, but the police and private security have eyes everywhere,