Notes on Navigation: Latitude and Longitude: The Geographic Grid

In order to measure accurately the position of any place on the surface of the earth, a grid system has been set up. It pinpoints location by using two coordinates: latitude and longitude. B. It is purely a human invention, but it is tied to two fixed points established by earth motions: the poles, or ends of the earth's rotational axis. 

1. Longitude represents east-west location, and it is shown on a map or globe by a series of north-south running lines that all come together at the North Pole and at the South Pole and are the widest apart at the equator -- these lines of longitude are called "meridians." Figure 1 -- meridians of longitude

2. Latitude represents north-south location, and it is shown on a map or globe by a series of east-west running lines that parallel the equator, which marks the midpoint between the two poles all around the earth's circumference -- these lines of latitude are called "parallels." Figure 2 -- parallels of latitude