GPS Global Positioning System. A system of satellites that allows one's position to be calculated with great accuracy by the use of an electronic receiver. A bad knot that was probably tied in error, will not necessarily hold fast, and may be difficult to untie. A course that is the shortest distance between two points, following a great circle . Great circle routes usually do not look like the shortest route when drawn on a flat map due to deviations caused by trying to draw a flat map of a round object such as the earth.
Any circle drawn around the earth such that the center of the circle is at the center of the earth.
The shortest distance between any two points on the earth lies along a great circle. A can buoy . A cylindrical buoy painted green and having an odd number used in the United States as a navigational aid. At night they may have a green light. Green buoys should be kept on the left side when returning from a larger body of water to a smaller one.