Requires a base or reference line. Direction is defined as angular deviations from or along this base line. Eeven southern hemisphere maps usually put north at the top. The direction to the north pole of the axis of earth rotation. A line from any point on the earth to the north pole is called a true north base line.
Meridians are true north base lines.
Unlike TN, GN does not point to a real place. Put on maps to make it easier to measure angles. GN lines run parallel, meridians converge to the poles. GN declinations are noted on good maps. Iin theory, the compass needle always points to the magnetic north pole.