First, your coords are definitely off, I'm seeing people get killed out in the sea.
The black arrow isn't pin point but it was to give an idea of a much higher elevation.
From what I've gathered X is North and South, Z is East and West, and Y is elevation.
The ingame coords (/do coords) for the locations are the same but in KM (except the Y access, it uses Meters still, further proof this is likely elevation). Example for the West (Left) most cord the ingame is "6.655KMx 349My -4.3KMz"
Also the 6662 one might be slightly off, that structure currently isn't in the game, there's evidence where it should be but not as easy to pin point as the hanger or the Northern shack by the road.
If you'd like more information you can PM me here or add me on steam. I also hang out on the playrust.net teamspeak (ts.playrust.net)
EDIT: I added 2 more locations, one far in in the North West and one South West on a mountain.