These lines serve as an imaginary grid that geographers use to pinpoint locations on earth. The lines of latitude, called parallels, appear horizontal and run east and west around the globe. The lines of longitude, which appear vertical and run between the North and South Poles, are called meridians. The Equator is the parallel that divides the globe into two halves, the Northern and Southern Hemispheres. Any point on the globe below the equator has a negative value for latitude, while points above the equator have positive latitude values.
Longitude is measured East or West of Greenwich, and can be expressed in different ways.
The choice of sign for longitude is also somewhat arbitrary. To determine the latitude of a particular location, geographers measure distance in degrees north or south from the Equator. To determine longitude, geographers measure distance in degrees east or west of the prime meridian, which passes through Greenwich, England. For greatest accuracy, longitude is also given in degrees, minutes, and seconds. The global address of any place on earth includes both latitude and longitude.