Flying over north pole became quite popular due to great circle routes going that way. use of GPS in civilian aviation actually came from compass getting confused during polar flight resulting in heading reversal. GPS satellites also supported polar operations from the start as the critical user needed flights over north pole. (this is one of those cases where typical map projections confuse people).
That said, magnetic compass deviations are common all over the world due to things like iron ore veins, so maps have corrections available.
GPS isn't used for altitude in aircraft in practice, it's too inprecise - barometric altimeter plus radar altimeter are the precise instruments for that.
> use of GPS in civilian aviation actually came from compass getting confused during polar flight resulting in heading reversal
Do you have a source for that? I was under the impression that INS-based navigation was much more precise than for that to have been an issue by the time GPS became available to civil aviation.
While GPS was apparently always planned to be provided for civilian navigation, Korean Air Flight 007 being shot down due to error in navigating over north pole led to explicit mention by White House:
KAL007 was an usage error of the INS mode of the aircraft's autopilot, though, which was itself working as designed (although that design was a bit of a footgun in retrospect).
The exact same error could have happened for a Pacific crossing near the equator. Magnetic aberration being larger near the poles had nothing to do with it.
That said, magnetic compass deviations are common all over the world due to things like iron ore veins, so maps have corrections available.
GPS isn't used for altitude in aircraft in practice, it's too inprecise - barometric altimeter plus radar altimeter are the precise instruments for that.