The Geographic Reference System consists of latitude and longitude. This system
treats the globe as if it were a sphere or spheroid. The sphere is divided
into equal parts called degrees. Each degree can be further subdivided into
60 minutes, each composed of 60 seconds. The standard origin is where the
Greenwich Prime Meridian meets the Equator. All points north of the Equator
or east of the Prime Meridian are positive. Each line of longitude runs north
and south and measures the number of degrees east or west of the Prime Meridian.
Values range from -180 to +180 degrees. Lines of latitude run from east to
west and measure the number of degrees north or south of the Equator. Values
range from the North Pole, at +90 degrees, to the South Pole at -90 degrees.