After studying Campanus' sphere and other polyhedra inscribed in a sphere it seems natural to me to develop a simple map of the World.
Roughly speaking the Earth rotates around an imaginary axis that passes through two points on the Earth's surface called North Pole and South Pole.
The Equator is the intersection between the Earth and a plane perpendicular at the midpoint of it axis.
The circles of latitud are parallels to the equator. They are called parallels because of that. The circles of latitude get smaller as the distance from the Equator increases
Latitude is a measurement of the distance north or south of the Equator. It is measured in degrees. The equator is defined as 0 degrees, the North Pole is 90 degrees north, and the South Pole is 90 degrees south.
Circles of longitud are great circles that passes through the two poles. They are known as meridians. One important (and arbitrary) meridian runs through the Royal Observatory in Greenwich, England. We call it the Prime Meridian.
Longitude is measured in degrees east or west of the prime meridian The prime meridian is assigned the value of 0 degrees.
Latitude and longitude lines are a grid map. A geografic coordinate system so we can now locate every point on Earth by specifying both latitude and longitude.
Playing with the interactive application you can rotate the Earth and control the number of parallels and meridians you want to see.
Hugo Steinhaus - Mathematical Snapshots - Oxford University Press - Third Edition (p. 197)
Peter R. Cromwell - 'Polyhedra', Cambridge University Press, 1999.