Suppose someone at sea reported that they were located on the 20°N line of latitude. A first question would be "where on the 20° N line are you?" After all, the 20°N line goes all the way around the world - more than 23,000 miles!
To locate places exactly on a globe or map it is necessary to have north-south lines - lines of longitude - that cross the east-west lines of latitude. Once it is known where the lines cross, any place on the globe can be given an exact location.
Some important facts about lines of longitude:
Lines of longitude are imaginary lines that extend from the North Pole to the South Pole.
Lines of longitude are not parallel. All the lines meet at the North Pole and the South Pole.
All same-numbered east or west lines of longitude are equidistant apart at the equator.
All lines of longitude are measured east or west of the prime meridian. Prime meridian is a way of saying the 0° line of longitude.
Lines of longitude are often shown on maps as being 10° apart at the equator. Sometimes they are shown as being 15° apart, or even 30° apart. How they are spaced and numbered depends on the purpose of the map.
The numbering of the lines continues for 180° to the east, and 180° to the west, for a total of 360°, a full circle.
The prime meridian and its continuation on the other side of the world, 180°, divides the world into two equal parts: The Eastern Hemisphere and the Western Hemisphere.
Locating places with lines of longitude
The lines of longitude on the diagram below are 15° apart. Notice that some of the lines are not numbered, that there are blank boxes on those lines. Study the numbers on the other lines, then print the proper numbers in the boxes.
What are the longitudes of the following points shown on the map? Remember: You must write E for east, or W for west to properly identify the location.
Every place on the earth is in two hemispheres (except for places on the prime meridian, 180° line of longitude, the equator or at the North and South Poles.