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Maps
are graphic representations of the Earth. Cartography is the art
and science of expressing the known physical features of the earth
graphically by maps and charts. No one knows who created the first
map, but we have the military to thank for refining maps and designing
GPS systems because of their demands for accuracy and detail.
Map
Coordinates
Coordinates are a mathematical way of defining a point or a region.
Map
coordinates are usually shown in one of two ways: the geographical
coordinates, given as latitude and longitude values in degrees,
minutes and seconds; or the grid coordinates, given as
easting and northing values, in metres. The geographic coordinates
system aligns with most Global Positioning Systems (GPS).
Scale
Scale refers to the relationship between the size of the map and
the actual size of area that is mapped. If the scale of a map
is 1:100,000, then one centimetre on the map would represents
100,000 centimetres, on the ground. For this reason, a scale of
1:25,000 would show much more detail than a map with a scale of
1:50,000 or 1:100,000.
Unfortunately, detail is not always practical, especially for
maps that cover large areas, because they would be ridiculously
large and impossible to handle.
Contours
Contour lines, or some people like to call them, the 'squiggly'
lines you see on the map are there to indicate the contour and
elevation in the landscape. Basically, the closer the lines are
together, the steeper the landscape.
Latitude
& Longitude
Latitude and longitude is the most common grid system used
for navigation. It will allow you to pinpoint your location with
a high degree of accuracy. Latitude is angular distance measured
north and south of the equator (equator is 0 degrees). As you
go north of the equator, the latitude increases all the way up
to 90 degrees at the north pole. If you go south of the equator,
the latitude increases all the way up to 90 degrees at the south
pole. In the northern hemisphere the latitude is always given
in degrees north and in the southern hemisphere it is given in
degrees south.
Longitude works the same way. It is angular distance measured
east and west of the prime meridian (prime meridian is 0 degrees).
As you go east from the prime meridian, the longitude increases
to 180 degrees. As you go west from the prime meridian longitude
increases to 180 degrees. The 180 degree meridian is also known
as the international date line. In the eastern hemisphere the
longitude is given in degrees east and in the western hemisphere
it is given in degrees west.
UTM
UTM stands for 'Universal Transverse Mercator', and is similar
to latitude and longitude except that it uses a different style
of output for recording coordinates. TMR utilises the UTM method
of recording way points. This means that you will more than likely
need to set your GPS to UTM mode, and datum WGS84 if you wish
to use any of the way points or coordinates on this site as they
are all specifically recorded in Australia for Australia.
The
UTM system works by breaking up the entire globe (earth) into
friendly usable zones. Each zone is labelled with a number that
refers to a region of longitude which is 6 degrees wide; and a
letter that refers to a region of latitude which is 8 degrees
high. Here is a visual example produce by Peter Dana of how the
globe is broken into zones.
If
you were to zoom in on the Australia, this is what you would see:
If
you further zoomed in to Victoria (SE Australia), you would be
able to see the finner details of the zoning system used in UTM
coordinates.
Victoria
is split down the middle by 2 zones (West Victoria - 54H and East
Victoria - 55H). This means any time your are entering a UTM coordinate
into your GPS and it requests a zone, you will need to enter either
54H or 55H depending on what part of Victoria your in.
So,
a typical set of fully specified UTM coordinates within Victoria
Australia would look something like this: E 578315, N 0789240,
UTM Zone 54H, Datum WGS84.
GPS
The basic idea behind a GPS is that orbiting the earth are
a thousands of satellites. Of these, about 24 are designed for
navigation. By reading signals from at least two satellites, a
GPS receiver is able to provide you with your location (3 or more
satellite signals are required to provide you with your location
if you are moving).
In
order for GPS to work, its antenna needs to receive the signals
from the orbiting satellites. Therefore, you need to be outside
with a view of the sky. Mountains, trees, buildings and other
obstacles can block the satellite signals or cause the signals
to bounce around creating positioning inaccuracies. When you turn
on the GPS unit, it will take some time for enough information
from the satellite to be processed before your position is "fixed"
or known. The weather can also effect the time required for a
fix.
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