Longitude is the angular distance of any point measured east or west on the Earth's surface. Meridians are vertical longitude lines, while parallels are horizontal latitude lines.
Meridians, or vertical longitude lines, converge at the poles and are widest at the equator. Greenwich, England is known as the Prime Meridian. It serves as a reference point for other longitudes and is designated as zero degrees. Longitude values are expressed in degrees, and the degrees are divided into minutes and seconds. Longitude values indicate the angular distance between Greenwich and points east or west of it on the surface of the Earth.