Something I'm not feeling in the hotel area of Pittsburgh is there seems to be magically spawning bandits.
I know I cleared an entire floor, moved up a level, was stalking a dude then Ellie gives me the "watch out behind you" and a dude came up the stairwell. This resulted in being shot in the back and then at least 10 guys pouring in from everywhere. It's really irritating how one guy blows your cover the whole damn area comes in. To be fair this is the only section so far that this has happened, and it's a huge area in and outside the hotel, so it could be expected that a gunshot would bring lots of attention.
They dont magically spawn at all. Each area has a set number of enemies. You just arent scouting the area well enough for them. Also, some enemies that are really close wont show up as a silhouette if youre using listen mode so occasionally they can be tough to spot and easy to be ambushed by. It helps immensley to throw a bottle or brick occasionally to grab the attention of whoever is around. This gains you the advantage of seeing the numbers and forming a plan to take them out.