Coordinate Systems - Magellan GPS Tracker User Manual

Coordinate Systems

Positions are locations that are described in a unique way so that one loca-
tion 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 twelve different coordinates systems; LAT/LON (latitude and
longitude), UTM (Universal Transverse Mercator), TD, OSGB, Irish Grid,
Swiss Grid, Swedish Grid, Finnish Grid, German Grid, French Grid,
MGRS and User Grid. 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/
0 0 W
LON is the most commonly used coordi-
0 0 .
1 1 5
nate system today. It projects lines of lati-
tude (parallels) and lines of longitude (me-
ridians) onto the earth's surface. Lines of
latitude are the equator and the horizontal
t
lines that are parallel to it. Lines of longi-
tude are the vertical lines that are perpen-
dicular to the equator and pass through the E
poles. A position is described as being the
intersection of a line of latitude and a line
of longitude.
Specifically, a position is up to 90 degrees north or south of the equator
(up to the poles, which are 90˚N and 90˚S; the equator is 0˚ latitude), and
up to 180 degrees east or west of the Prime Meridian, which is 0˚ longi-
tude. (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 pro-
viders. On land, you may find that UTM coordinates are easier to use
than Lat/Lon.
Instead of projecting an imaginary grid of intersecting lines onto the globe,
UTM projects sections of the globe onto a flat surface. Each of these sec-
tions is called a "zone." There are 60 zones to cover the entire earth be-
tween 84˚N and 80˚S (polar areas are not described by UTM). Each zone
is 6˚ wide as projected from the earth's center.
72 Magellan GPS Tracker