Simplify the following text for a Grade 6 native English-speaking person.
Original: The longitude of other places is measured as an angle east or west from the Prime Meridian ( specifically , it is the angle between a plane containing the Prime Meridian and a plane containing the North Pole , South Pole and location in question ) .
Simplified: ( A meridian is an imaginary line drawn from the North Pole to the South Pole . ) Longitude says how far east or west of the Prime Meridian any place is .