Basic Map Reading and Orienteering Workshop

Trillium: ADF Spring Gathering 1999

A. Map Reading

Brief introduction – What is a map?

1. Types of Maps

A reduced representation of the surface of the earth.  (tell Steven Wright joke about an actual size map).

a. planimetric – literally translated means “flatground measurement”

Planimetric maps are common, most road maps are planimetric.  These types of maps are usually designed to represent manmade features.  Generally they poorly represent natural features.  Think of how well a road map denotes a mountain, with a point, a name, and maybe an elevation at the summit. 

b. orthophotos – example of photomosaic of the Cabin Camp #5 area.

Aerial photographs have distortions, especially around the edges of the photo, that make their use as navigational maps unreliable.  Orthophotos are aerial photographs that have these distortions corrected, so that they accurately represent distances on the ground.  Orthophotos, especially when used in conjunction with a topographic map, can provide very detailed information to navigate or find landmarks.  A good orthophoto map will allow you to differentiate different stands of trees or even in some cases individual trees.  Unfortunately orthophotos are expensive, but they are becoming more readily available, now available for download off the internet for much of the country. 

c. topographic – represents both natural and manmade features usually in good detail.

Topographic maps depict terrain and elevation, water features, and sometimes vegetation, as well as man-made features like roads and buildings.  They are generally very detailed and are usually derived from aerial photographs or orthophotos.  Contour lines are used on topographic maps to depict elevation. 

2. Parts of a Map – using example of USGS 7.5 minute topographic map

a. name/area of coverage – Joplin, VA

b. description

c. date, revision date – 1966, photorevised 1971, photoinspected 1981

d. legend – see minimal example on Joplin quadrangle

e. direction (North arrow) – True North, Grid North 1° 31’, Magnetic North 7 1/2° W declination

See handout with 16 point compass rose.

f. distance/scale – 1:24,000, also see the graphic scale on the topo map

g. contour interval (only if topographic map) – 10’ on the Joplin quad

h. map projection & coordinate system – Universal Transverse Mercator zone 18

Note size of USGS quadrangles are in multiples of 7.5 minutes of longitude and latitude.  The Joplin quad is 7.5 minutes by 7.5 minutes (a minute is 1/60th of a degree of lat/long).  See the USGS handout on “Universal Transverse Mercator (UTM) Grid.”  Note that projections are somewhat advanced concepts, and when you are more experienced at map reading, the projection may be something that you will want to consider in more detail. 

3. Types of Scale Presentation

Scale: The proportion between a distance on the map and the actual distance on the ground.
See the USGS handout “Map Scales.”

a. graphical – see Joplin quadrangle for example

b. verbal statement – i.e. 1” = 1 mile (see Joplin quad for example)

c. representative fraction – ratio of 1 to some number

The larger the fraction, the larger and clearer the details, and the smaller the area covered by the map.  The first number, always “1” represents the map distance.  The second number (i.e. 24,000) represents 24,000 of the same units on the ground. 
Representative fractions can be translated to verbal statements fairly easily.  i.e. 1:24,000 è 1”  (on the map) = 24,000” (on the ground) è 1”  = 24,000”/12 (12 inches in 1 foot) = 2,000’. 
Topographic maps of scales 1:63,000 and lower ratios can be used for navigation on foot, but scales of 1:24,000 and lower are generally best.  Common USGS topographic map scales are 1:250,000, 1:100,000, 1:24,000.  Orienteering maps are often 1:15,000 to 1:10,000. 

4. Map Interpretation

a. symbols – see USGS handout “Topographic Map Symbols”

Go over a few relevant examples, such as buildings, streams, perennial streams, wetlands.  On orienteering map go over some additional symbols like cliffs, boulders, etc.

b. colors

c. topography

• Contour lines connect points of equal elevation.
• Slope steepness can be determined by the spacing between contour lines.  The closer the lines the steeper the slope.  Show example on Joplin quad.
• There are two types of contour lines
•                 Index lines – usually darker brown & have elevation labels
•                 Regular lines – lighter brown without labels
• The contour interval may vary from one map to another, and the units may also vary.  Often map distances are in meters, but vertical distance (elevation) is sometimes in feet. 
• Explain how to tell hills from valleys, and depressions.
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B. Navigation

1. Using a map – Setting an Azimuth

• Introduction to and parts of the compass
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• Types of compasses
• basic compass
• orienteering compass (with or without mirror for sighting)
• military compasses – these are generally designed for durability and precision.
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• Compass Parts
• Baseplate – transparent so you can see the map through it, usually has ruler(s), scale ruler(s), directional arrows marked on it, lines for orienting the compass on the map.
• Housing or dial – it rotates, it has compass rose and degrees marked on it, N arrow lines and needle “box.”  Some compasses have declination adjustments marked on the housing.
• Needle – red end is pointing towards magnetic N
• Mirror or sighting mechanism
• Note: Beware of metal objects near the compass when you are using it to navigate.  Watches, rings, metal plates in your head, etc.
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a. Map Measurements

1) measuring distances from maps

• Using scale bar and ruler, or piece of paper to create a small ruler in map units (use feet or meters), or put masking tape on edge of compass and mark map units on it.
• Use preset rulers on compass to measure map distance.  Many good map reading/orienteering compasses will have these built in scales.
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• Exercise 1: Practice measuring distances between points on the map.  See worksheet.

2) measuring direction (azimuths) from maps

• See handout with representation of the geographic difference between True North and Magnetic North, and declination map of North America.

a) Declination – the angle between direction the compass needle points (that is, magnetic North) and true North.  Compasses really don’t point North, not true North at least.  Unless you live on the line where the difference between True North and Magnetic North are the same.  (Have them determine where that line is on the map, and then have them determine the approximate declination adjustment for our location.)

There are at least 4 ways to deal with this problem.

1) draw lines on your map that represent magnetic North instead of true North – this method makes it much easier to accurately navigate if your compass doesn’t have built-in declination adjustment

2) adjust your bearing each time you measure a bearing from the map.  West declination – add, East declination – subtract. Discuss declination adjustment in VA – see handout

3) use a compass that has a declination adjustment.  They have a small screw that allows you to offset the compass housing from true N. 

4) ignore it!  If you choose to do this, keep in mind that you may be off by fairly large distances.  We could do some Trigonometry to calculate how far off you can get, but just take my word for it.  “This is only an option when declination is 1 to 2 degrees or less.” 

b) Method 1

• Draw a straight line on the map through your location and your destination, extending it across the map (this is not necessary, see method 2 for a quicker way).
• Align arrow on baseplate of compass with line between points.  Then turn the compass housing until the line denoting north on the compass housing are lined up with the north-south lines on the map.  You have now “set” the compass.
• At this point if you have not drawn magnetic north lines across your map you will need to add your declination adjustment to get the correct bearing. 
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c) Methods 2

• Use edge of baseplate to align compass with start and destination points.  Align N arrow lines on compass housing with N lines on map to “set” the compass. 
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• Exercise 2: Measure 2 or 3 bearings between points on the map, and check their progress.  See worksheet.

** Head Outside for Remainder of Class **

b. Orienting the map for navigating

• Method 1 – inspect the map and your surroundings, turning the map so that the features on the map line up with the features in the area.
• Method 2 – determine where N is with the compass and line up N on the map to N on the compass.  Keep in mind that N is not always the top of the map. 

c. Finding your location on a map

Using topography and prominent landmarks

• Use hills or valleys, streams, lakes, and other landmarks like fire towers, radio towers, buildings to determine your position.  – this often requires good map reading skills.
• Read compass bearings from landmarks to determine your location
• Use 2 or more landmarks that are visible from your location.  Take bearings from them using your compass.  Transfer the bearings to the map, by drawing lines from the landmarks on the map along the compass bearings you measured.  Your location should be where the 2 lines intersect. 
• Exercise 3: Have them orient the orienteering map to the surroundings & determine their location based on landmarks.  Use detailed map of camp area for this exercise. 

2. Using a Compass - Following an Azimuth

a. Determining Ground Distance

• Use a  Pace Course to learn pacing ground distances.  Counting your steps or your paces is usually the best way to keep track of how far you have traveled. 
• Do pace course.  1 – at least 100m of flat, open ground. 2 – 50 meters of thick, rougher terrain. 3 – 50 meters each of uphill and downhill.
• Exercise 4: Estimate ground distance using pacing.

b. Holding and Orienting the Compass properly

• Hold the compass flat. 
• When setting a bearing make sure that the compass housing is “dialed” so that the North end of the compass needle is in the box (or between the lines on the housing). 
• When getting a compass reading to follow a bearing, make sure you rotate your whole body with the compass.  This is a common error of the novice. 

c. Following an Azimuth

• Exercise 5: 3-legged compass walk
• Drop a marker on the ground where you are standing.
• Set the desired bearing on the compass.  Start with any number from 0 to 120°.
• Choose a distance to pace, from 10 to 50 meters.  Use this distance for each leg of the compass walk.
• Go x meters @ bearing.  Stop
• Go x meters @ bearing + 120°.  Stop.
• Go x meters @ bearing + another 120°.  Stop.
• You should now be back where you started, or close to it. 

d. Reading an Azimuth from Landmarks

• Orient yourself and the compass (rotate your whole body) till you are facing the landmark or destination. 
• Aim the compass directly at the landmark.
• While aiming the compass, hold the baseplate firmly in your hand, and rotate the housing on the compass until the N end of the needle is in the “N box” on the housing.  Make sure you line up the correct end of the needle (this is a common mistake).
• Why would you want to set a bearing on a destination that you can see.  For example, if you are trying to get to the top of a hill that you can see in the distance.  As you walk along, you may go down into a valley where you can no longer see the hill.  By setting the bearing to the top of the hill on the compass you can then use the compass to be sure that you are traveling in the right direction.
• Note: If you are translating azimuths from the compass to the map, remember to subtract W declination and add E declination, the opposite of when you are reading bearings from map to compass.
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• Exercise 6: Practice this technique with targets that are in easy view.

e. Overcoming Obstacles while following a bearing

• If you encounter an object or land feature that you cannot walk through or over, such as a stream or thick shrubbery, then you’ll have to walk around.  This is problematic because it takes you off of the bearing that you were following.
• Locate a prominent point on the other side of the obstacle that falls along the bearing that you are following. 
• Walk around the obstacle, find the point on the other side and resume your original course. 
• Remember to pace or estimate as closely as possible the distance from where you left your course to go around the object to the point where you returned.  Make sure to add this amount into the distance that you have traveled. 
• You can use your compass to sight backwards across the lake or other obstacle to make sure you are in the correct spot. 

Sidestepping trees or shrubs can be accomplished by moving left or right 90° from the bearing (you can use the compass turned sideways to determine 90°) a certain distance necessary to avoid the tree.  Then once past it, move back 90° in the opposite direction, keeping the distance that you sidestepped before and after the same.
Exercise 7: Try these methods on a small scale in the field. 

3. Using Map and Compass Together

Finding locations on the ground with only a known starting point, points marked on a map, and a compass

a) determine current location and destination (on map)

b) set compass bearing (from the map)

c) determine ground distance to the to the destination (measure on the map)

d) Orient yours self and the compass (together) in the field along the direction of travel that you set on the compass in the previous step

e) following the bearing, pacing the required distance

Exercise 8: Navigate the orienteering course laid out by the instructor.  Answer the question about the destinations along the course to demonstrate that you found the way points.