Reference Lines on Earth, Continued
Meridians of longitude are the great circles. They all pass through the
center of Earth. The prime meridian or 0° of longitude is the starting
point for all longitude measurements. Longitude is measured in same
manner as latitude except that it is measured east or west throughout
180°. The prime meridian is also known as the Greenwich meridian. It
is so named because is passes directly through Greenwich, England.
Latitude and longitude comprise the terrestrial or geographic coordinate
system. Figure 1-9 illustrates how a position is located on a chart. We
will discuss the mechanics of plotting a position on a nautical chart later
in this chapter.
Before we can do that we have to learn more about the
charts we use.
Figure 1-9. Locating a position on a nautical chart.