Aerial View Of Airport Runway

A runway can normally be used in two directions, which means the runway may have two names: "runway 33" and "runway 15". The two numbers always differ by 18 (= 180°).
El Dorado International Airport, Runway 31R/13L
Runways in North America that lie within the Northern Domestic Airspace are, because of the magnetic North Pole, usually numbered according to true north.