Magellan eXplorist XL - Manual (Page 77)

69
Coordinate Systems
Positions are locations that are described in a unique way so that one
locations cannot be confused with another. This is done by using a
coordinate system to describe locations. Your Magellan receiver has the
ability to use any one of four different coordinates systems; LAT/LON
(latitude and longitude), TD (Time Difference of Arrival), UTM (Universal
Transverse Mercator), and OSGB. The one you select (in SETUP) will be
determined by the maps and charts you use; you would generally want
the receiver to display position coordinates in the same system that is
used by your maps.
LAT/LON Coordinate System. LAT/LON is the most commonly used
coordinate system today. It projects lines of latitude (parallels) and lines of
longitude (meridians) onto the
earth’s surface. Lines of latitude
are the equator and the
horizontal lines that are parallel
to it. Lines of longitude are the
vertical lines that are
perpendicular to the equator
and pass through the poles. A
position is described as being
the intersection of a line of
latitude and a line of longitude.
Specifically, a position is 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.
UTM Coordinate System. Another commonly used coordinate system
is UTM (Universal Transverse Mercator), which is generally found on land-
based maps and quad sheets that are produced by government map
providers. On land, you may find that UTM coordinates are easier to use
than Lat/Lon.
EQUATOR
0
°
P
R
IM
E
M
E
R
ID
IA
N
0
°
Latitude
L
o
n
g
it
u
d
e
115
° 00.00W
42 °
30.00N