They call that line of longitude the prime meridian . Its address is zero degrees longitude, or 0 o longitude. From the prime meridian, you can travel west halfway around the Earth to the 180 o east longitude line. Look at the globe to the left. Notice that the lines of longitude do not stay the same distance from each other.
Meridians are the farthest apart at the equator.
They are closer together at the poles. In fact, one degree east-west is 69 miles at the equator. At the poles there is no distance between each degree line. Learn about some of the projections used in mapmaking today. Take a look at our Projection Animations page.