Which way do lines of longitude run and what do they measure? lines of longitude run east to west and measure places expressed in degrees north or south of the prime meridian. lines of longitude run east to west and measure places expressed in degrees north or south of the equator. lines of longitude run north to south and measure places expressed in degrees east or west of the prime meridian. lines of longitude run north to south and measure places expressed in degrees east or west of the equator.