The 180° longitude line, located in the opposite direction of the prime meridian (0° longitude), is called the International Date Line. If we circumnavigate the entire world, our clock undergoes a difference of 24 hours (180° East – 180° West), thus there is a difference of 1 day in both places. The journey from east to west will decrease one day and the journey from West to East will increase one day. In order to overcome this difficulty, different nations have unanimously determined the international date range with reference to the 180° longitude line.

Importance of International Date Line: Taking reference from the International Date Line, the date is determined all over the world. 

Its importance can be understood through the following points:

1. This line removes the variation in time of 1 day that occurs upon circumnangating the earth, out to be revolving around the world-which is the difference of one day. 

2. Due to the assumption of daybreak (dawn) in accordance to this line, the determination of the day in the world becomes simpler. 

3. Travelling from east to west of the international date line, time decreases by 1 day. While travelling from west to east, one day increases. 

4. If the international date line is not determined, then the same date cannot be found across the world.