We can identify locations as precise points on the Earth's surface by using a grid system of latitude and longitude. The use of giving a north and south direction (latitude) and an east and west direction (longitude) is used through the world. This system aids us in measuring distances and finding directions between and among places on the Earth's surface. The starting point is the prime meridian, with represents 0º longitude. The exact opposite position at 180º is called the International Date Line, which is where the date actually changes. So if you are going from Monday in California, and cross the International Date Line going to Japan. It would be Tuesday! You have to start the day somewhere.