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:

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  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

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.