Maps are drawn based on latitude and longitude lines. Latitude lines run east and west and measure the distance in degrees north or south from the equator (0° latitude). Longitude lines run north and south intersecting at the geographic poles. Longitude lines measure the distance in degrees east and west from the prime meridian that runs through Greenwich, England. The grid created by latitude and longitude lines allows us to calculate an exact point using these lines as X axis and Y axis coordinates.
Both latitude and longitude are measured in degrees (°).
1° = 60 minutes
1 minute = 60 seconds
7 ½ minutes = 1/8 of 60 minutes = 1/8 of a degree
15 minutes = ¼ of 60 minutes = ¼ of a degree