<P> The International Date Line (IDL) is an imaginary line of navigation on the surface of the Earth that runs from the North Pole to the South Pole and demarcates the change of one calendar day to the next . It passes through the middle of the Pacific Ocean, roughly following the 180 ° line of longitude but deviating to pass around some territories and island groups . </P> <Dl> <Dd> This description is based on the most common understanding of the de facto International Date Line . See § De facto and de jure date lines below, and map at right . </Dd> </Dl>

What is the purpose of the international date line