Longitude lines are vertically arranged lines that extend from north to south. They are based on the prime meridian, which is measured as 0 degrees longitude. The prime meridian is also known as the Greenwich meridian as a result of its extending through the London suburb of Greenwich. Longitude lines are also referred to as meridians and each one extends from the North Pole to the South Pole. Therefore every meridian is the same length.
Size decreases from the equator toward the poles.
The International Date Line is a line that partly corresponds to the 180th meridian. It is a line that extends through the middle of the Pacific Ocean. See Figure 2.3 on page 21 of the text for the location and change of day that results. Maps are two dimensional, selective, reduced and distorted images of the earth. They are distorted because, being two dimensional, they are attempting to represent the real three dimensional earth.