The surface intersection of any plane that cuts a sphere exactly in half is the largest circle that can be drawn on the surface of a sphere. These are known as great circles. Any circles produced by planes that do not cut through the centre of earth are smaller than great circles and are called small circles. Great circles have important properties with respect to such global subjects as navigation (shortest distance between any two points on the earth’s surface), global positioning, and the subdivision of earth (parallels and meridians).