Runway heading refers to the magnetic direction in degrees that corresponds to the centerline of the runway. Runway headings are in increments of ten degrees and no more than two numbers. They are oriented to magnetic directions and are named for the numerical increments of a compass or circle ranging from 010 degrees to 360 degrees. For example, a runway oriented to the magnetic direction "360" would be named "runway 36". On the actual runway itself, the numbers 36 would be painted just after the runway threshold to clarify the proper runway heading for approaching and departing planes.
Runway headings always come in pairs due to the fact that there are two ends to a runway. They are separated by 180 degrees. For example, if there is a runway with a runway heading of 270 on one end, the opposite end would have a runway heading of 090. Since the magnetic poles are constantly changing, the magnetic heading for a runway can change. While most of the time, the runway heading corresponds directly to the magnetic heading, there are times when the magnetic heading and the runway heading vary. Due to the change occurring, a runway heading is determined by either rounding up or down the magnetic heading closest to it. For example, a runway with a magnetic heading of 271 degrees would have a runway heading of 270 degrees and be named runway 27.
Pilots can be cleared to "fly or maintain runway heading" directly after takeoff. This means they are expected to fly the runway heading and not the magnetic heading for the centerline of the departure runway. The runway heading is used by pilots in pre-flight calculations to determine the best runway for takeoff, landing distances, and crosswind, headwind, or tailwind strength. The runway heading is also used in developing approach and departure procedures, instrument approach procedures, and vectors laid out by air-traffic control for pilots approaching or departing the airport's airspace.