Circle of latitude Circle of latitude A circle of latitude on Earth is an abstract east–west circle connecting all locations around Earth (ignoring elevation) at a given latitude. Circles of latitude are often called parallels because they are parallel to each other; that is, any two circles are always the same distance apart. A location's position along a circle of latitude is given by its longitude. Circles of latitude are unlike circles of longitude, which are all great circles with the centre of Earth in the middle, as the circles of latitude get smaller as the distance from the Equator increases. Their length
Rhumb line ship's latitude could be established accurately by sightings of the Sun or stars but there was no accurate way to determine the longitude. The ship would sail north or south until the latitude of the destination was reached, and the ship would then sail east or west along the rhumb line (actually a parallel, which is a special case of the rhumb line), maintaining a constant latitude and recording regular estimates of the distance sailed until evidence of land was sighted. The surface of the Earth can be understood mathematically as a Riemann sphere, that is, as a projection of