Here's why:

* Longitude: Lines of longitude run from the North Pole to the South Pole, measuring distances east or west of the prime meridian.

* Prime Meridian: This is the starting point for measuring longitude. It's an imaginary line that runs from the North Pole to the South Pole, passing through Greenwich, England.

* 0 to 180 Degrees: Longitude is measured from 0 to 180 degrees, with:

* 0 degrees being the prime meridian.

* 180 degrees being the International Date Line (the opposite side of the Earth).

Let me know if you have other questions about geography!