This is much like de-
scribing a position in a
city by the street inter-
section, but "Fifth and
Main" can describe
more than one location,
since these are com-
monly used designa-
tions. Lat/Lon uses
numbers and hemi-
sphere to describe each
position in a unique
way. Using Lat/Lon co-
ordinates, no position
can be confused with
any other.
In Lat/Lon, positions are
described as being so
many degrees north or
south of the equator (up to the poles, which are 90°N and 90°S; the equator
is 0° latitude), and so many degrees east or west of the Prime Meridian, which
is 0° longitude. (The Prime Meridian passes through Greenwich, England.)
Parts of a degree are minutes; there are 60 minutes (written as 60') to a
degree. Minutes can also be divided into smaller units. Fractions of a minute
can be expressed as decimals or as seconds. (There are 60 seconds to one
minute written as 60"). So a Lat/Lon position coordinate can be expressed in
two ways, which your Magellan GPS receiver displays as 25°47.50 or
25°47'30.
The Magellan GPS receiver can also display coordinates in another common
coordinate system — UTM, or Universal Transverse Mercator. UTMs are
described at the end of this section.
Using Position Fixes to Record Your Movement
A
position fix
is the coordinates of a location as determined by your GPS
receiver, positioning with a map and compass, or some other orientation
technique. lt "fixes" your position to a specific place. If the fix is saved (either
by writing it down or by storing it in the receiver's memory), the fix becomes
a
waypoint.
The difference between a fix and a waypoint is that the waypoint
can be recalled for use at a later time.
Imagine that you are camping in the area illustrated on the next page. Before
setting out to explore the area, you determine the position of your camp
(latitude/longitude) by obtaining a position fix, which you store as waypoint
2
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