We need to know where we are located. We need to be able
to communicate that to others.
The reasons for this are obvious: so we can direct others to a location or be directed to where
we are needed. There are systems for navigating. The one we are going learn is simple and easy.
We will learn a system called Universal Transverse Mercator, UTM, adopted in 1947.
Mercator was a man who lived in the 1512-1594. He devised the system that bears his name.
This is the name of the system we use. First they divided the surface of the earth up into pieces
that can be managed easily on a flat surface. Starting at the international date line, they divided
the world into 60 zones. Each zone is 6 degrees. You can see the US mainland goes from
Zone 10 to 19 in the chart below. We here in Oregon have two zones 10 and 11,
the 120 degree being the the line that separates the two.
To make each zone understandable from a map perspective they placed
a line down the center
of the zone called the Meridian. This line has a value of 500,000. There are parallel lines
placed next to the Meridian every 1000 meters. Also horizontal spacing of lines placed every
1000 meters, creating a grid overlay. If we travel to the west of the Meridian line, the number
of the grid line decreases by 1000 meters or a unit of one.
Traveling east of the Meridian the numbers go up.
Schroeder Park Map
Print the Schroeder Park Map so you will have it to refer to.
You can see that the Search and
Rescue Building in Grants Pass is located between the vertical lines that read 471 000 and 472 000.
Actually the 471 is not labeled but 470 and 472 are. You can see the fairgrounds and SAR
house plainly. The number 470 000 m E is an EASTING number. If you go east or west
of the Meridian the number is still called your EASTING. We read numbers on the grid from
the lower left corner. Reading them to the right and up. So the line number to the left of the
Race Track at the Fairgrounds is 471 ooo m E, meaning we are 29 kilometers west of the
Meridian in Zone 10. To be in the center of the letter "O" in the word "fairgrounds" in the
center of the track, we would say our Easting was 10 T 471 627. The 10 is for the zone.
The "T" is for the horizontal zone which we will discuss in a bit. The 471 is for the line to our
left and the 627 is for how many meters we are to right of the 471 vertical line of the grid square.
Verbalizing this is more difficult than looking at the map. Seeing that, we are now placed on a
vertical line, on the surface of the earth, to an accuracy of one meter. Think about that for a
moment before we go on. That is a line, with an accuracy to some 39 inches on the whole
of the planet's surface and we can tell some one, or know for ourselves where we are.
There are Horizontal bands of 8 degrees. These bands start at
80 degrees in
the southern hemisphere and stop at 84 degrees in the northern hemisphere. These
Bands are lettered from "C" to "X" omitting letters "I and "O" so as not to be
confused as numbers. Here in Grants Pass, Oregon we are in Band T and our northing
number is 4, 697 000 meters north of the Equator. Starting at the Equator for us in
the northern Hemisphere, with a value of Zero. There are parallel lines every 1000
meters. It is as simple as that. We read our map from the lower left corner of
the grid square. Find the numbers on the Map edge, they tell you where you are.
See in the upper right hand corner of the map it reads Horizontal Band T, and at
vertical line number 472. Most of your TOPO maps have the UTM ticks on them
if not the grid lines. Most of us will deal with maps of comparatively small
areas, the idea of zones will fade as we concentrate on the superimposed grid
system of 1000 meter squares that have assigned values.
You can see that these grid squares are an easy way to name your location.
Here is a map you can see how to read from the lower left corner.
Using a grid tool or by interpolation you can see how the number reads.
Always use a scale of 1:24 000
See the Corner Scale
Using the Grid scale is an easy way to fix your location. With
practice you will be
able to interpolate where you are by dividing with your eye, half and half and half
is 125 meters and so forth. Close enough to find a spring or trail. You will want
a grid scale for SAR work.
You can find these on line. They are clear plastic and they work
Now there are some things I did not tell you. How the top and
the bottom of the
world use Universal Polar Stereo graphic projections. That at the equator each
zone of 6 degrees has a minimum and maximum Easting value from 160,000 to
834,000. At 84 degrees a 6 degrees zone has a value of 465,000 to 515,000
Easting. That the top Northing band has 12 degrees instead of 8 degrees.
To avoid Negative numbers locations south of the equator, the equator was
assigned a value of 10,000,000 meters for the Southern Hemisphere.
The Equator has a value of Zero for the Northern Hemisphere. Some northing
numbers are valid numbers both north and south of the equator, so to avoid
confusion we have the lettered bands. Not many of us really need to know all of this.
You now it least heard it once.
What we need to know to set up our GPS is this. Use NAD27
(that is) North
American Datum 1927 or your GPS may say NAD27 CONUS. This puts your
GPS using the same DATUM as the TOPO map. Use Maps with a scale of
1:24, 000. Set your GPS to Meters. Set it to UTM, not Longitude and Latitude.
Your GPS is a radio receiver and a computer. The antenna needs to see the sky.
If it can tell you your location in UTM, it is a good GPS. They do not have to be
expensive. You can put yourself on the map. Let the GPS give you your UTM.
You can find where you are.
Set your compass up with the correct declination for your location.
In Search and Rescue most use Silva Ranger or Brunton Classic 8040 G.
Let me say here that the order of importance, for navigation is
then GPS. For navigation and safety, the Map is first. Do not go out into the
woods without a map of where you are. Do not go on a search without a map
of the search area with UTM.
The first purpose of the compass is to proof the map.
The second function of the compass is to take bearings
To set the map right with the world we use a compass. This is
to proof the map.
By having the map correctly oriented on the ground we can usually fix our position
by observation. This is done by placing the map on the ground with the open
compass on top of the map. Set the bezel on the compass to 360 degrees.
Line up the vertical lines on the map with the side of the compass. Rotate the map
till the red needle is outlined in red. All the vertical lines are now pointing North.
The second function of the compass is to take bearings. Taking
a Bearing is simple.
Hold the compass level and site across it using the sights or ports provided to view
the object of interest. Turning the bezel to align the red needle with the red outline.
Now you can read the numbers on the outer bezel for your bearing. On being directed
to travel on a bearing, we first rotate the bezel of the compass to that bearing number.
Then, using the mirror and sights, rotate you body till the reddened lines up with the red
outline. You are now sighting at that bearing.
Fixing your position
After proofing the map you can fix your position with the compass.
At this point you can spend some time to look at the map and your view of your
surrounding. By careful observation you should be able to pick out feature on the
landscape and relate them to the map. By taking a bearing on that object
(hill top usually) you can transfer a line through the object on you map
(without moving the map). By taking a second bearing of another object you
should be able to place another line though the second object.
Where those two lines intersect is where you are.
Magnetic North and True North
The north pole is on the move, the magnetic north pole that is, take
look and see why we have to set our compass up so that when we line up
the needle and the out line for magnetic north that True North is where
it should be! Look on a map for magnetic declination. By setting this
declination we calibrate the compass to our general location. No longer
do we have to add or subtract the error between True North and
Magnetic North. In Search and Rescue we use True North.
Red is the color of the needle that points North.
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