The runways at all airports in the world has two numbers on it at the opposite ends. Have you ever wondered what they mean? These numbers indicate to pilots the runways to be used for takeoff and landing and the same is communicated to the pilots by the air traffic control. Each of these numbers corresponds to a direction on the compass.
The numbers are always between 01 and 36, signifying between 10 degrees and 360 degrees on the compass. The difference between both the numbers is always 18, which signifies 180 degrees on the compass. 180-degrees because it is the complete opposite.
The first digit in the number uses the actual bearing and the second digit is rounded off to the nearest degrees. The last number in the degree is always dropped.
So if a runway number is 27, it means that the direction of the runway is 270-degrees from North. Even if it is 268-degrees, it will be rounded off to 270 degrees.
Bigger airports with parallel runways like the O' Hare airport in Chicago and the Los Angeles International Airport, etc have their runways painted with the same numbers. Such runways also get an alphabet after the number signifying left, centre or right.
If there are two runways facing 320-degrees, it will be named 32L and 32R. The opposite side would be 16R and 16L. Sometimes, the airports will have to change the numbers owing to the shift in the earth's magnetic field. Earth's changing magnetic fields can alter the magnetic north.
The geographic North Pole of the earth remains at the same location with the Longitude at 12.726567 and Latitude at 89.852595.
The magnetic North Pole though shifts once in a long period. The magnetic north is what gives a compass' reading, hence changing the reading which gives the runway its numbers.
The Tampa airport's runway, Florida airport's runway, etc have all had runway number changes. The FAA (Federal Aviation Authority) checks the reading of every airport once in five years and changes are made if necessary.
There is much more to the world of aviation than meets the eye. There is great detail hidden in even seemingly small things like the marking on a runway. There's a reason for aircraft to even change the direction in which they take off and land. This depends on the wind direction and you can read about it here.