Meridians and Parallel
On a map or chart, geographic coordinates are defined y two
sets of great and small circles. The great circle set is the circles that all
pass through the north and south geographic poles. These are the MERIDANS OF
LONGITUDE.
The other set is a series of circles each established by a
plane cutting through the earth perpendicular to the polar axis. The largest
circle is the equator and is mid-way between the poles. Theses circles are
called the PARALLELS OF LATTITUDE.
Coordinates are measured in degrees and one degree is 1/360th
of a complete circle. The degrees are measured from the PRIME MERIDAN which is
the 0 degree mark and this meridian goes through Greenwich, England. The longitude
of any position on earth is described as so many degrees East or West of the
Greenwich line.
Parallels of latitude are measured in degrees north
or south of the equator. To give more or greater precision to a location, the
degrees are subdivided into MINUTES. There are 60 minutes in one degree.
One degree of latitude is equal to 60 nautical miles
and this means that one minute of latitude is one mile. You need to note that the distance between the
meridians are not a fixed constant
distance and distance cannot be figures using the meridian degrees. Meridians
get closer together as they move north and south of the equator.
The system is logical and it can let you pinpoint a position
on the globe.
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