http://m.pcgamer.com/2012/10/08/dishonored-how-to-get-low-chaos-no-kills-and-ghost-ratings-no-spoilers

This article has me confused. I was under the belief that as long as you hid bodies your chaos wouldn't go up. So what is the truth of the matter? Which exact factors cause chaos to go up and which ones cause it to go down. And is there any point to hiding bodies aside from other npc's not finding them. Does hiding them affect chaos at all?

well its sort of true, if you hide the body, it won't alarm the guards so less chaos, chaos factors in guard kills,civil kills, founded bodies etc, so if your in a tight space, go hide the body or use the ash power if your going to kill the person

I believe as long as bodies are NOT found, you can leave them wherever. At least, in my case, I've left a few bodies around in plain
sight after I knew there was no one around to stumble on them, and still got low chaos for the level.

Factors that increase chaos rating:

------ Killing guards / civilians / weepers (if you knock them out and then they get eaten by rats or fall into river and drown, that still counts as
a kill)

------ Bodies being discovered, alarms being triggered

Those are the biggest ones, I believe.

I just noticed after finished a level that I got an overall Chaos rating, as opposed to one for the level.

Is that always the case?

There's a detailed overview of how chaos works in a pinned thread in the spoiler forum: http://www.gamesas.com/topic/1415443-notes-on-stealth-detection-chaos-and-trophiesachievements/

Edit: looks like the article in the OP is a copy/paste of the info in the thread I linked. But it's formatted better in the thread