International Date Line International Date Line The International Date Line (IDL) is an imaginary line of demarcation on the surface of 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. The IDL is roughly based on the meridian of 180° longitude, roughly down the middle of the Pacific Ocean, and halfway around the world from the Greenwich meridian. In many places, the IDL follows
Longitude Act and that of 1774 halved the amount offered for any method or instrument achieving the degrees of precision outlined in the original Act (i.e. £5,000 for a degree, £7500 for 2/3 of a degree or £10,000 for 1/2 degree). The 1818 Longitude Act, which completely revised the composition and remit of the Board of Longitude, again changed the rewards, by now offered for improvements to navigation in general rather than simply for finding longitude. In addition, the Act outlined rewards for navigating the North West Passage, again on a sliding scale from £20,000 for reaching the Pacific through a north