Grid and Bear It - Geography - page 32

Starting from the equator, each successive line (degree) of latitude is numbered consecut-
ively both to the north and to the south as far as the North Pole (Latitude 90° North) and South
Pole (Latitude 90° South).
Except for the equator, each line of latitude is identified by a number between 0 and 90 and
by the word North or South (or the abbreviations N or S) to indicate its location north or south
of the equator. Thus, the line that is 20 degrees north of the equator is referred to as Latitude
20° North. It would be misleading and incomplete to just call this line “Latitude 20” because
another line of latitude south of the equator could also be called “Latitude 20.”
Only one line of latitude is a great circle, a line that divides the Earth in half.
Longitude
The system of longitude lines has the following characteristics:
Lines of longitude run from the North Pole to the South Pole (top to bottom of the map)
and are called meridians.
As opposed to latitude, no two lines of longitude are parallel to each other. Rather, suc-
cessive lines of longitude are about 70 miles apart at the equator, but from there they slowly
converge until they come together at the two poles (see Figure 3-2).
The prime meridian (Longitude 0°) divides the world into the Eastern Hemisphere and the
Western Hemisphere.
Starting from the prime meridian, every line (degree) of longitude is numbered consec-
utively to the east and to the west half way around the world. Because Earth is 360 degrees
around, 180 degrees of longitude lie east and west of the prime meridian.
Every line of longitude (except the prime meridian and the 180 degree line) is identified by
a number from 1 to 179, and by the words East or West (or the letters E or W) to indicate its
location east or west of the prime meridian. Thus, the line that is 20 degrees east of the prime
meridian is referred to as Longitude 20° East. It would be misleading to call this line “Longit-
ude 20” because some another line that is 20 degrees west of the prime meridian also could be
called “Longitude 20.”
Every line of longitude, is a great circle — a line which, if continued around the world,
would divide the Earth equally in half.