This all assumes you have an iPhone.
Put your phone on a stable, level surface. Open the compass app and see what degree it is pointing towards.
Without moving your phone go to settings-> compass and turn on/off “True North” and go back to the compass app.
You will probably notice a few degrees difference between the two.
“True North” is the place we have all agreed upon as the North Pole, and same for the South. These true points are not in the precise same location as the magnetic pole.
As everyone else has explained, GPS is based upon True North. This just helps you experiment with it yourself.
GPS is not based on earth’s magnetic field at all, it is bases on signals from satellites in earth orbit. GPS devices can have a magnetic field sensor to determine the direction they point but is not relevant for determining the position.
There is ways to determine the north without using the magnetic field, gyrocompasses use forces produces when the earth rotates and points to the geographical north pool not magnetic. That has been the standard on larger ships since WWI
If you navigate with magnetic compares the moment of the magnetic poles can be a relevant factor so it where on earth you are and you need to compensate for it. There is maps on the difference of magnetic and true direction
https://upload.wikimedia.org/wikipedia/commons/1/11/World_Magnetic_Declination_2015.pdf
Because of the location of the magnetic poles, the moment in a year has a minimal effect because the long-distance makes the direction change minimal in most places.
The satellites that broadcast the signals that your GPS device triangulates (essentially) do _not_ shift around like the Earth’s magnetic field. They’re up in space, nothing to affect them in orbit outside of space debris or natural orbit decay (but by the time any of them drift out of orbit really, they’ll be replaced anyway). The physical North Pole of the planet that _their_ coordinate system refers to doesn’t move.
The Earth’s magnetic field is created by all the gooey molten iron in the Earth’s core; its not of consistent composition and it keeps moving around, so the net magnetic field it produces moves as the molton core moves and changes.
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