What determines when a location is 'CLEARED' on the map?

In Skyrim, an area became cleared if you killed the boss in that area or most of the enemies in the area.

Don't see why it should be any different in Fallout 4.

I have cleared areas on missions and also just by stumbling into them and exploring. I have found if your on a mission or not, after killing most enemy's, the area will show as cleared on the map. Not all enemy's need to be dead for the area to be clear which is misleading as I have been tricked by that before (false sense of security). Some places that don't have a boss like the supermarket still read as clear when most enemy's are dead or wounded.

It would be nice if areas remained clear as it really ruins immersion when you have played a part of the story where you have to clear an area and you fast travel there later and the people are back. It's also ANNOYING because it's clears on the map and is presumed safe. I dropped into the ironworks today and was attached by the forged who I killed on a story mission. As soon as I spawned in I got a Molotov to the face!

I am wondering if there are one or two left over somewhere, the area may not stay clear. Has anyone observed similar occurances?

I also have varied situations. I have returned to certain locations on my map which aren't labelled " clear" . Some after re killing enemies a second time it " cleared" . Some areas in which you need to return to for a quest won't " clear" until all enemies are killed and quest completed. Some areas just cannot be " cleared" after returning multiple times, most original enemies remain dead however a small amount respawn. Even after killing them it still won't " clear" and I have searched every inch in that location.

First, Settlements can in fact be cleared. Both my husband and I both have cleared Red Rocket which is a settlement. So lets just put that myth down.

From my experience, you can get an area marked as cleared if you kill everything the first time you engage an enemy in a location. This does not count if they shoot you and you run away. But as soon as you land a hit (from what I have seen) you have to clear the area before you leave. I am doing further tests to prove this theory.

So killing the boss does not clear the area. Killing most of the most of the enemies does not clear a location. You must kill all the enemies in a given location before it will be marked clear and prevent enemies from respawning. If an area isn't cleared some of the loot will respawn too so sometimes it might be a good idea to leave a location uncleared and come back later for an extra helping of loot.

Killing the final boss, as others have stated, would make sense, except that it doesn't seem to hold completely true. I ran through the Corvega Assembly Plant, killed the final "boss," Jared, and my map never told me it was Cleared. However, after a second trip to the area, after some time had passed, enemies had respawned and I got to kill all the Raiders again, this time, however, the map told me it was "Cleared."

Personally, I hope they leave certain locations in the game un-Clear-able, it's always fun to go back and fight more Raiders. If every location is cleared, there are no more fight-clubs to go and fight in. So far, Corvega and Ironworks are two locations I've explored that never said they were "Cleared" even after killing the final boss.

As a possible theory, it might have to do with the number of missions pertaining to a location. The first time I "Cleared" Corvega was for the quest: The First Step. The second time I went there was for the quest to plant the MILA device at the top for Tinker Tom. After that mission was done, my map told me the location was "Cleared." So it's possible that the locations are labeled Cleared when you've completed all quests that involve the location, but that's just a theory. Highly flimsy at that, as I understand there's a BoS quest that involves Corvega as well.