Quoted:
I live in the Phoenix area. It's relatively flat with a few hills and a few buildings over one or two stories, but the streets are very straight and flat. If law and order completely broke down it would be possible to take a 400 yard shot in some places and not be observed. Obviously, if you're the guy stomping around with a scoped AR thinking you're Duke Nuk'em, things are going to catch up to you.
That's kinda funny, because the phoenix area is exactly what I was envisioning. I grew up there. I remember when I was a kid, with a bb gun. I thought I was being sneaky. I'd shoot stop signs from my roof. I'd shoot trees and fence posts and "other things."
If you went back there now, you could go probably easily see exactly where I was shooting from by looking at the 'activity' and forming a center.
Sure, in your scenario, a few pop shots here and there aren't likely to blow your cover. But if you're working repeatedly in the same AO, a determined foe will be able to track you. Like bosnia countersnipers.