What exactly contributes to chaos?

So, I just did a run through, trying to be low chaos. I choked out or otherwise knocked out just about everyone (patrolling guards, nosy maids, etc). I killed maybe about 25 people who I didn't have to kill for missions, and that was right at the beginning. I was never full-out detected at any point, no one ever noticed a corpse or body and put the place on high alert. I was very careful, yet I still have high chaos. How can this be? Does choking people out contribute to higher chaos? Because if so, that makes no sense.