Latitude is the angular distance from the Earth’s equator and is expressed as either north or south. Longitude is the angular distance from the Greenwich meridian and is expressed as east or west.
Latitude
The largest latitude circle is the equator itself, which is zero degrees. Other latitude circles are parallel to the equatorial plane, and grow smaller nearer the poles. You can imagine a toy with bottom most ring as equator (Figure 1). The earth is divided into two hemispheres : Northern and Southern . The northern circles are marked as 0º to 90 º N and southern circles are marked 0 an 0º to 90 º S. All the circles are parallel to each other so these are sometimes referred to as parallels (Figure 2)
Longitude
Longitude circles are not parallel to each other, but pass through both poles and intersect the equator perpendicularly. All longitude circles are great circles of equal diameter. The prime meridian, which equals zero degrees longitude, is the longitude arc from the North pole to the South pole that runs through Greenwich Observatory in England. The longitude arc 180 degrees opposite (the other half of the same great circle) is the international dateline. Longitudes are measured in degrees east or west of the Greenwich meridian (Figure 3).
Figure 3 Longitude measurement (http://www.physics.miami.edu/huerta/class/110/110_gif/LATITUDE_LONGITUDE_MERIDIA.GIF
