Geodetic longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is measured in degrees, with the prime meridian at Greenwich in London serving as the reference line at 0 degrees. Longitude values range from 0 to 180 degrees east and west of the prime meridian. Longitude is essential for navigation, mapping, and understanding global positioning. It works in conjunction with geodetic latitude, which measures north-south position. Together, these coordinates help define precise locations on the Earth's surface, facilitating various applications in fields like cartography and geography.