The imaginary lines that run north and south on a map are called meridians.

Here are some key things to remember about meridians:

* They all converge at the North and South Poles.

* They are used to measure longitude.

* Each meridian represents a specific degree of longitude.

* The Prime Meridian (0° longitude) is the starting point for measuring longitude, passing through Greenwich, England.

Let me know if you'd like to know more about meridians or longitude!