There are a few issues at play here: some examples are
1:
If X is the north face of something Y
X, the face, is approximately a Plane;
Y is a three-dimensional object that is not a sphere.
If Y is translated to a different location, then the coordinates of the points lying on X will likewise be changed.
2:
To say that a point X is north of a point Y broadly describes their relative location but does not require that the precise coordinates of X or Y be known; nor is it necessary to know the precise distance.
There are also different possible interpretations of north Of.
The second interpretation is considerably less precise, but is the probably the more common intention:
"Captain Smith, you will lead your company through the phase line running between those two hills to the north."
"But Major, those hills aren't directly north of us."
" I stand corrected. Captain Smith, you will advance through the phase line running between those two hills to the north. "
Simon
[I'm ignoring the problems that occur around the north or south pole. Too many shoggoths].