The angular measurement from the centre of earth determines the lines of latitude on its surface. An added advantage is that one minute of latitude is equivalent, for all practical purposes, to 1 nautical mile. 1 degree to 60 nautical miles. A nautical mile is 1854 metres, for the metrically inclined. It has always been fairly easy to find one's latitude from the position of the sun or, if in the Northern hemisphere, from the pole star.
Longitude Imagine the earth as a large orange.
Slice the peel into gores as if you were about to peel it. The distance of a degree of longitude varies with the place on earth it is measured. By determining one's latitude and longitude a position anywhere on earth can be described. The compass allows a bearing to the point to be determined and the chart is where all these come together to allow us to determine our position. In practice a number of methods are employed.