Longitude is the angular distance around Earth from a reference plane that defines a prime meridian. A meridian is synonymous with a line of longitude. Some conventions apply to angular expressions of longitude. One is that the angle is expressed counterclockwise with respect to the view from the North Pole to the South Pole. Sometimes, the angle from the zero meridian is stated as a value from 0° to 360°. The other convention is to express the longitude as a negative value from 0° to −180° west from the prime and as a positive value from 0° to +180° east of the prime. Longitude can be expressed in a variety of units (radians, grads, semicircles, arc seconds, or mils) and formats (+/- or E/W, to ...