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Wednesday, May 4, 2011

Finding your Way with Map and Compass.

Finding your Way with Map and Compass.
How to use a Compass and Topographic Map?
compass (or mariner's compass) is a navigational instrument for finding directions on the earth. It consists of a magnetised pointer free to align itself accurately with Earth's magnetic field. A compass provides a known reference direction which is of great assistance in navigation. The cardinal points are north, south, east and west. A compass can be used in conjunction with a clock and a sextant to provide a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient.

compass can be any magnetic device using a needle to indicate the direction of the magnetic north of a planet's magnetosphere. Any instrument with a magnetized bar or needle turning freely upon a pivot and pointing in a northerly and southerly direction can be considered a compass. A compass dial is a small pocket compass with a sundial. A variation compass is a specific instrument of a delicate type of construction. It is used by observing variations of the needle. A gyrocompass or astrocompass can also be used to ascertain True north.
topo map
topographic map tells you where things are and how to get to them, whether you're hiking, biking, hunting, fishing, or just interested in the world around you. These maps describe the shape of the land. They define and locate natural and manmade features like woodlands, waterways, important buildings, and bridges. They show the distance between any two places, and they also show the direction from one point to another.
Distances and directions take a bit of figuring, but the topography and features of the land are easy to determine. The topography is shown by contours. These are imaginary lines that follow the ground surface at a constant elevation; they are usually printed in brown, in two thicknesses. The heavier lines are called index contours, and they are usually marked with numbers that give the height in feet or meters. The contour interval, a set difference in elevation between the brown lines, varies from map to map; its value is given in the margin of each map. Contour lines that are close together represent steep slopes.
Natural and manmade features are represented by colored areas and by a set of standard symbols on all topographic maps. Woodlands, for instance, are shown in a green tint; waterways, in blue. Buildings may be shown on the map as black squares or outlines. Recent changes in an area may be shown by a purple overprint. a road may be printed in red or black solid or dashed lines, depending on its size and surface.
Maps are made to scale; that is, there is a direct relationship, a ratio, between a unit of measurement on the map and the actual distance that same unit of measurement represents on the ground.
From Here to There: Determining Direction.
To determine the direction, or bearing, from one point to another, you need a compass as well as a map. Most compasses are marked with the four cardinal points—north, east, south, and west—but some are marked additionally with the number of degrees in a circle (360: north is 0 or 360, east is 90, south is 180, and west is 270). Both kinds are easy to use with a little practice. The illustrations on the reverse side show how to read direction on the map.
One thing to remember is that a compass does not really point to true north, except by coincidence in some areas. The compass needle is attracted by magnetic force, which varies in different parts of the world and is constantly changing. When you read north on a compass, you're really reading the direction of the magnetic north pole. A diagram in the map margin will show the difference (declination) at the center of the map between compass north (magnetic north indicated by the MN symbol) and true north (polar north indicated by the "star" symbol). This diagram also provides the declination between true north and the orientation of the Universal Transverse Mercator (UTM) grid north (indicated by the GN symbol). The declination diagram is only representational, and true values of the angles of declination should be taken from the numbers provided rather than from the directional lines. Because the magnetic declination is computed at the time the map is made, and because the position of magnetic north is constantly changing, the declination factor provided on any given map may not be current.
Taking a compass bearing from a map:
Draw a straight line on the map passing through your location and your destination and extending across any one of the map borders.
Center the compass where your drawn line intersects the map border, align the compass axis N-S or E-W with the border line, and read on the compass circle the true bearing of your drawn line. Be careful to get the bearing in the correct sense because a straight line will have two values 180° apart. Remember north is 0, east is 90, and so on.
To use this bearing, you must compensate for magnetic declination. If the MN arrow on the map magnetic declination diagram is to the right of the true north line, subtract the MN value. If the arrow is to the left of the line, add the value. Then, standing on your location on the ground, set the compass so that "zero degrees or North" aligns with the magnetic north needle, read the magnetic bearing that you have determined by this procedure, and head off in the direction of this bearing to reach your destination.
compass and map
compass and map
(1) Drawing a straight line over the map edge
(2) Reading the compass on the map
Compass readings are also affected by the presence of iron and steel objects. Be sure to look out for - and stay away from pocket knives, belt buckles, railroad tracks, trucks, electrical lines, and so forth when using a compass in the field.
How to use your Watch as a Compass?
To use your watch as a compass, one must think in terms of the ordinary clock face. That is, a round clock with numbers 1 through 12.

When you need a rough compass, simply point the hour hand (or the part of your watch where that hour would be if it wasn‚t digital) at the sun.

Half way between that point and the 12:00 point on your watch points to the south. For example, if it is 8:00, point the 8 at the sun and south would be at the 10:00 position.

This will work, even if it is a cloudy day and you are not sure where the sun is. To find where the sun is, simply hold a pencil or stick upright over a light piece of paper or a lighter part of the ground or a light rock. Even on a cloudy day the stick or pencil will cast some kind of shadow.

As in using any compass, you'll need to keep rechecking which way is south. If you want to go east, simply go at a 90 degree angle to the right of south. North is opposite from south. West is 90 degrees to the left of south.




    


Topo Map Skills

A Topographic Map includes contour lines drawn to represent changes in elevation. When you follow a path on a topographic map that crosses these contour lines, you will be either climbing or descending. A path running parallel to contour lines is relatively flat.

When reading a topographic map, you need to visualize in your mind's eye a 3-dimensional view of what the symbols and contour lines are representing.
The most important thing to remember is that CLOSE contour lines mean STEEP terrain and OPEN contour lines mean FLAT terrain.
Shaded relief added to a topographic map makes it more realistic and helps visualize the real landscape.
For example, see how the mountains and canyons stand out on this map:



What is the elevation of Mt. Passaconway? _______________
What is the elevation of Mt. Tripyramid? _______________
The closest Index contour line for both peaks is 3,000 feet. You can see another Index line of 2,000 feet. There are 4 Intermediate lines between 2000 and 3000 so each intermediate line represents a 200 foot change in elevation.
Counting up from 3,000 feet, there is 3200, 3400, 3600, 3800, and the top line is 4000 (actually the next index line).
So, both peaks are over 4000 feet and it looks like Mt. Tripyramid is possibly almost 4200 feet high.

This example of a very simple topographic map shows many common features. Keep your eyes open to see these features on other maps and you will start to understand how a topo map works.

Even without elevation numbers, clues that #1 is a hill include streams converging away from the hilltop, contour lines pointing sharply towards the hilltop (indicating draws), contour lines pointing widely away from the hilltop (indicating rounded ridges).

Using contour lines, you can tell a lot about the terrain, including steepness, ruggedness, and ground cover. On the image above, look at point A. There are no contour lines around this location so it is relatively flat here and a good place for a campground by the lake. You can tell from the elevation listed at marker 3095 that the campground is at 10155 feet.
You can also tell the elevation change between each contour line by looking at the Index lines. Notice that the Index line near point B is labeled 11600 feet and the one due north of it is labeled 10400 feet - that is a difference of 1200 feet. Between these two Index lines are two more Index lines so each index line represents a change in 400 feet of elevation - 10400, 10800, 11200, and 11600.
Count the lines between two index lines and you should see there are 4 lines which cause the 400 feet between the two index lines to be divided into 5 intervals, each one being 80 feet in elevation. So, now we know that on this map every contour line represents 80 feet of elevation change.

If you follow a single contour line, your elevation remains constant. For example, starting at point X and following the Index line to the NorthEast, around, and down South to point Y, you would stay at about 10,800 feet.

When you cross contour lines, you are either hiking up or down. Look at the two routes to get to the peak at point B - the red route and the blue route. Each path reaches the top, but the blue route is three times as long as the red route. That means it covers more distance to gain the same elevation so it is a more gradual slope - and probably an easier hike. Going up the red route may require a lot of scrambling and hard work.

Using the map above, pretend you are camped at the Grandview Campground but you heard there is great fishing in Willow Creek at point C over the mountain to the SouthEast. How could you get there?
Well, a straight line to the SouthEast would be shortest on the map, but would include a climb of over 1500 feet!
Instead, heading East from camp and circling the north side of the mountain will result in a longer distance covered but only about 325 feet in elevation! That may be a much better hike.
One other thing to take into consideration. Notice that the ground is colored green up to about the 10,800 foot index line. The white area above that is open ground while the green area is forested. This can be good or bad. The forest can offer shade and coolness, but on the other hand it may be thick and difficult to navigate.

  

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