Adventist Youth Honors Answer Book/Recreation/Orienteering

1. Explain what a topographic map is, what you expect to find on it, and three uses for it.

Topographic maps are also commonly called contour maps or "topo maps." Topographic maps conventionally show topography, or land contours, by means of contour lines. Contour lines are curves that connect contiguous points of the same altitude. In other words, every point on the marked line of 100 m elevation is 100 m above mean sea level.

Other than showing elevation via the contours, you can also expect a topographic map to show any important landmarks, such as rivers, lakes, and roads. They will often also show railroad tracks and major power lines (and their towers). Power lines are especially handy because the towers are visible from great distances and each represents a point on a map (whereas a road or river would represent a curved line). These attributes make them ideal for pinpointing position.

Topographic maps have many uses, letting a competent user determine any of the following:

• Where he is.
• How to get where he wants to go.
• What the terrain is like in a given area (steepness, for example).
• Where a river comes from and goes to.
• The route a hiking trail follows.
• The location of campsites.
• The distance between to points.
• Elevation of a mountaintop.
• Latitude and longitude of any point on the map.
• What areas may be susceptible to avalanches or flooding.

2. Identify at least 20 signs and symbols used on topographic maps.

These symbols are used by the U.S. National Park Service:

• 

  Airport

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  Boat launch

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  Campground

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  Canoe access

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  Drinking water

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  First aid

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  Fishing

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  Food service

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  Four-wheel drive access

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  Gas station

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  Hospital

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  Information

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  Litter receptacle

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  Lodging

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  Parking area

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  Picnic area

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  Ranger station

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  Recycling

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  Restrooms

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  RV campground

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  Self-guiding trail

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  Shelter

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  Store

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  Telephone

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  Trailhead

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  Bridge

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  Hiking trail

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  Marsh

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  Parking area

• 

  Rapids

• 

  Spring

• 

  Unpaved road

3. Give the nomenclature of an orienteering compass.

Lensatic Compass

The lensatic compass consists of three major parts: the cover, the base, and the lens.

a. Cover

The compass cover protects the floating dial. It contains the sighting wire (front sight) and two luminous sighting slots or dots used for night navigation.

b. Base

The body of the compass contains the following movable parts:

1. The floating dial is mounted on a pivot so it can rotate freely when the compass is held level. Printed on the dial in luminous figures are an arrow and the letters E and W. The arrow always points to magnetic north and the letters fall at east (E) 90° and west (W) 270° on the dial. There are two scales; the outer scale denotes mils and the inner scale (normally in red) denotes degrees.

1. Encasing the floating dial is a glass containing a fixed black index line.

1. The bezel ring is a ratchet device that clicks when turned (on some compasses). It contains 120 clicks when rotated fully; each click is equal to 3°. A short luminous line that is used in conjunction with the north-seeking arrow during navigation is contained in the glass face of the bezel ring.

1. The thumb loop is attached to the base of the compass.

c. Lens

The lens is used to read the dial, and it contains the rear-sight slot used in conjunction with the front for sighting on objects. The rear sight also serves as a lock and clamps the dial when closed for its protection. The rear sight must be opened more than 45° to allow the dial to float freely.

4. Know the meaning of the following terms:

a. Elevation

The height of a point relative to sea level.

b. Contour interval

The elevation change between adjacent contour lines on a topographic map. If you travel from one contour line to another, your change in elevation will equal the contour interval.

c. Magnetic North

Magnetic North is the direction a compass will point, which is towards the North Magnetic Pole. The North Magnetic Pole is not the same place as the Geographic North Pole. The North Magnetic Pole is the point on the Earth's surface where the Earth's magnetic field points directly downwards. This pole is constantly wandering; its estimated 2005 position was 82.7° N 114.4° W.

d. Declination

The angular difference between magnetic north and true north (defined in reference to the Geographic North Pole), at any particular location on the Earth's surface, is called the magnetic declination. In other words, it's how far off a compass is from True North, or the correction that must be applied to a compass reading.

e. Scale

An important property of a map is the scale. It can be indicated by a scale bar and/or a ratio 1:n. This enables the map user to measure a distance on the map and determine the distance on the ground. These days maps are usually produced under the metric system which makes it easy to perform this task. Maps are usually produced at standard scale factors of (say) 1:10,000 or 1:50,000 or 1:100,000 and all you need to do is take a measurement on the map (in mm) and multiply that figure by the scale factor to determine the distance on the ground. However, maps from some countries may use imperial units, especially older maps. These maps displayed scale ratios but often they were of the form 60 chains (a chain is 22 yards, or 66 feet) to 1 inch or 2 miles to 1 inch, etc.

f. Measuring

The act of determining distance on a map and translating it to distance on the ground. In order to do this translation, you must know the map's scale (see above). Measuring can be done with a ruler or with calipers.

g. Back-azimuth

See under azimuth below.

h. True North

True North is the direction from any point on the Earth's surface to the Geographic North Pole.

i. Azimuth

The azimuth is a compass bearing expressed in degrees. There are 360° in a circle, and North is, by convention, 0° (or 360°). East is 90°, South is 180°, and West is 270°. While azimuth expresses the compass bearing in the direction of interest, the Back Azimuth expresses the compass bearing in exactly the opposite direction. In other words, azimuth is the direction to which you are going, and back azimuth is the direction from which you are coming. The back azimuth can be calculated by adding or subtracting 180° from the azimuth. Add if the azimuth is less than 180°, otherwise subtract.

j. Distance

Distance is the measure of length, or how far apart two points are away from each other.

7. Know two methods to correct for declination and when correction is necessary.

1. Set it and don’t worry about the declination unless you get a location with a different declination.
2. You can add or subtract the declination from the degrees shown on 360 scale of your compass.

When is correction necessary?

If you are any place in the world that is not the on the 0 line on a map.

9. Explain resection and its use.

Resection is a method of using a compass and a map to determine your current position. The first step is to find a feature of the landscape that you can also identify on the map. This could be a mountain peak, an intersection, a bridge, or even a utility pole (some topographic maps mark where high-voltage lines are, as well as the position of the poles that hold them up). The closer these two landmarks are to 90° offset from one another, the more accurate the resection will be. For instance, if the first landmark is at 115°, choose the second one as close to either 205° (115°+90°) or 25° (115°-90°) as you can. This is not a hard and fast rule, and the prominence of the landmark may well be more important than the 90° offset. Once you have shot an azimuth to the first landmark, calculate the back azimuth, and plot a line on your map from the landmark towards (and past) your current position (which should be somewhere on that line). Be sure to correct for declination when plotting this line. Then shoot the azimuth of the second landmark, and plot it's back azimuth on the map as well, again correcting for declination. If your readings are accurate and your plotting was done carefully, your current position should be very close to where these two lines intersect.

10. Prove your ability in the use of a map and/or a compass by following a one-mile (1.6 km) cross-country course with at least five given readings or control points.

Adventist Youth Honors Answer Book/Compass course