In aviation, runway numbers are based on their magnetic compass heading, rounded to the nearest 10 degrees and dropping the last zero. A runway designated as 17/35 is a single strip of pavement that can be used in two directions. When a pilot is taking off or landing on Runway 17, they are facing a magnetic heading of approximately 170° (South/Southeast). If the wind changes and they need to land from the opposite direction, the same strip of land is referred to as Runway 35, meaning the pilot is facing 350° (North/Northwest). Because runways are almost always built to align with prevailing local winds, and aircraft must take off and land into the wind for safety, the "active" end of the runway changes throughout the day. At very large airports with parallel runways, you might see letters added, such as 17L (Left) and 17R (Right), to distinguish between two runways pointing in the same direction.