Final answer:
Runways are numbered according to magnetic track in Eastern Domestic Airspace and true track in Western Domestic Airspace, due to variations in the Earth's magnetic field.
Step-by-step explanation:
Runways are numbered based on their orientation relative to magnetic north or true north, and this is influenced by geographical location. In Eastern Domestic Airspace, runways are numbered according to their magnetic track, while in Western Domestic Airspace, true track is used.
This is done because the Earth's magnetic field varies in different parts of the world. In the Eastern Hemisphere, the magnetic variation is such that using magnetic track is more practical for navigation. In the Western Hemisphere, particularly in the polar regions, magnetic variation is greater and less reliable for navigation, so true track, which is based on the geographic North Pole rather than magnetic north, is used to number runways.
Answering the student's question: Runways are numbered according to their magnetic track in Eastern Domestic Airspace and true track in Western Domestic Airspace.