Besides just putting up a map of Skyrim side by side to your own world map and comparing, what's a good way to ensure that you have discovered every location?? I recently discovered a remote cave 300 hours into a game and i was certain that i had charted everything.

Oh hell naw.

Last week it came as a total surprise to me that Whiterun has a Hall of the Dead.
I haven't even visited most of the caves and ruins I've found in my time.
Doubt I ever have a map with *CLEARED* written in every location that allows it.

It was actually quite some time before i first visited the Hall of the Dead in Whiterun myself.

Somehow I missed this one nordic ruin south of Riverwood..

I believe there are at least 350 marked locations. Some that change are the Imperial-Stormcloak Camps, they change when a hold has been taken over.

Then, there are some that never "clear".

The one i missed was a small cave north of Solitude and at the foot of the mountain that the Thalmor Embassy sits on.

There is a thread right below this one where it is claimed that there are 250 unmarked locations, not found on map..

well "points of interest" not really "locales" i guess

A "point of interest" would be the Eiffel Tower or the Statue of Liberty. Not Labyrinthian or Azura's shrine. Don't take the family there on vacation. Lol!!

You can try tmm 1 in the console to reveal them all and If you have a photographic memory you'll know which one you missed.

this cant be reversed with tmm 0 so just save before doing it.