The meridian 12° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Greenland, the Atlantic Ocean, Africa, the Southern Ocean, and Antarctica to the South Pole.
The 12th meridian west forms a great circle with the 168th meridian east.
Part of the border between Western Sahara and Mauritania is defined by the meridian.
12th meridian west Wikipedia
Starting at the North Pole and heading south to the South Pole, the 12th meridian west passes through: