Question

What is an imaginary line that runs along the middle of the earth dividing the north and south?

Answer 1

The answer is equator
the equator is an imaginary line that divides the north and south halves.
the prime meridian is an Imaginary line dividing the Earth east an west. (Sometimes called Greenwich Meridian because the line run through Greenwich, England.)

Answer 2

Equator or prime meridian