Lines of longitude can best be described as imaginary lines on the Earth's surface joining the north and south poles. They are also called meridians. These lines are numbered from 0° to 180°, with the Prime Meridian at 0°, which passes through the Royal Observatory in Greenwich, England.
Lines of longitude measure the distance of a place east or west of the Prime Meridian, which is used as the reference line for measuring longitude. The 180° meridian is exactly opposite the Prime Meridian and marks the International Date Line.
Each line of longitude is a great circle that runs from the North Pole to the South Pole, cutting the Equator at a right angle. Longitude is an important geographic coordinate that is used to locate positions on the Earth's surface, along with latitude, which measures the distance of a place north or south of the Equator.
Overall, lines of longitude help us to navigate and locate places on the Earth's surface, and are an important tool for understanding and studying geography.