A location is a rectangle on the map. Bring always tests against one, and unit creation and movement are addressed by one.
The key action is Move Location, which snaps a location onto a chosen unit. That is what gives you “around this unit”, and skill ranges, tracking and proximity checks are all built on it.
MoveLocation("Skill Area", "Terran Marine", CurrentPlayer, "Anywhere");
KillUnit("Men", P8, "Skill Area");If several triggers move the same location they will overwrite each other. Make a separate location per purpose; it is much safer.
One piece of old advice is wrong. Zergling, Science Vessel, Zealot and Dark Templar sit slightly above or below the grid when placed in the editor, and the folklore was to avoid them when moving a location onto a unit to save locations. Measured, they all land correctly: MoveLocation centres on the unit's real centre, not on where the editor drew it.