Longitude and latitude are angles that define points on a sphere. Together, the points compromise
a coordinate scheme that can locate or identify geographic positions on the surfaces of planets
such as the earth.
Latitude tells you where you where you are between the North and South poles. Latitude angles
can range up to +90 degrees (90 degrees north) and down to -90 degrees (90 degrees south).
Latitudes of of +90 and -90 correspond to the north and south geographic poles on the earth,
Longitude is defined in terms of meridians, which are half-circles running from pole to pole. A
reference meridian, called the prime meridian, is selected, and this forms the reference by which
longitudes are defined. On the earth, the prime meridian passes through Greenwich, England; for
this reason it is also called the Greenwich meridian.