ABSTRACT
The Earth can be considered as a sphere covered by a grid of lines called meridians of longitude and parallels of latitude. These lines are overlaid on maps of the planet’s surface to aid navigation. Parallels of latitude are all lines encircling the Earth, parallel to the equator (the parallel with the greatest diameter), from zero degrees (at the equator) to 90 degrees north (north pole) and 90 degrees south (south pole). Meridians are semicircles (each of the same radius) which connect the north and south poles. Opposite meridians form a complete Earth circumference, unlike the parallels of latitude. Longitude is measured up to 180 degrees west and east from the zero meridian (prime meridian) which passes through the Greenwich observatory in London.
