The imaginary lines perpendicular to the equator are called meridians.

Here's a little more about them:

* Definition: Meridians are lines of longitude, extending from the North Pole to the South Pole. They are all semi-circles, and they all converge at the poles.

* Purpose: Meridians help us determine the east-west position of a place on Earth.

* Key Meridian: The Prime Meridian (also known as the Greenwich Meridian) is the most important meridian. It is located at 0 degrees longitude and divides the Earth into the Eastern Hemisphere and the Western Hemisphere.

Let me know if you have any other questions about geography!