Here's why:

* Earth is a sphere: The Earth is a sphere, and we divide it into circles to make it easier to map and locate places.

* Longitude lines: Lines of longitude run from the North Pole to the South Pole, like slices of an orange.

* 360 degrees: A circle is divided into 360 degrees. So, we divide the Earth into 360 lines of longitude, with each line representing one degree of longitude.

Important Note: While there are 360 degrees of longitude, we typically refer to 180 degrees east and 180 degrees west, as the Prime Meridian (0 degrees longitude) divides the Earth into two hemispheres.