The circumference is the distance of the earth that is measured around the poles. Eratosthenes method of finding the circumference of a planet with the sun's rays cast a shadow on the equator a vertical stick of 2,500 km making an angle of 40° with the planet shows a distance of 40,075.017 km.
He also estimates that the meridian has a length of 252, 000 stadia. And described these techniques in his book measure of the earth.
