Compass and Topo Map Reading (PCEC)
Participants will learn compass- and map-reading skills.
4 or higher
Indoor instruction, outdoor for course practice
Potlatch Conservation Education Center at Cook’s Lake, Casscoe
Education Program Coordinator, 870-241-3373
30 minutes for basic compass, up to 2 ½ hours for compass and topo mapping
Suggested Number of Participants:
20 - 25
One adult supervisor per 10 students; outdoor activities, weather permitting.
- Learn how to read a compass.
- Learn to read a topography map and map orientation.
- Learn to use a compass and map readings to reach a destination.
*See glossary for definations
Map of area
Topographic map of area
New technology has provided the outdoor enthusiast with GPS (global positioning system) units that can pinpoint their location, track their movement and mark the spot where game or interesting natural features are found. Long before this technology, skilled adventure seekers used a compass and topographical map. The compass is a navigational instrument for determining direction relative to the Earth's magnetic poles. It consists of a magnetized pointer (usually marked on the north end) and aligns itself with Earth’s magnetic field. For centuries, the compass has greatly improved the safety and efficiency of travel. A topographical map, also called a topo map, tells you where things are and how to get there. These maps show the land’s contour or shape with contour lines in addition to features such as roads, rivers, lakes. Contour lines follow the ground surface at a constant elevation. Variations in color and the distance between contour lines help identify features such as slopes, waterways and buildings. Because topographical maps show the shape of the land, they are the most suitable type of map for most outdoor activities in lightly populated areas.
Prerequisite: Participants should understand the major points on a compass (NSEW), the difference between magnetic north and true north, and be able to recognize numbers between zero and 360.
How to read a bearing:
- Hold the compass just above the waist and keep your elbows firm against your sides, forming a triangle between the compass and both elbows. Place the compass in one hand; take hold of the compass dial with the thumb and forefinger of your other hand. Be sure the direction-of-travel arrow on the compass base plate is pointing towards your destination (away from you).
- Turn the dial until the N on the dial lines up with the north end of the magnetic needle. The magnetic needle will appear to be framed by the orienting arrow printed on the bottom of the dial.
- When alignment of the magnetic needle, orienting arrow, direction-of-travel arrow and your destination is perfect, read the bearing. Don’t move your head up and down to sight on your distant object (destination), just move your eyes. This helps you remain steady when aligning the compass.
- Your bearing is the number on the dial that lines up with your direction-of-travel arrow.
- To take a bearing that is perpendicular (90 degrees) from your first bearing, you would stay fixed in that spot where you read the first bearing and turn your body (holding the compass) towards the perpendicular direction you wish to go. Watching the magnetic needle on the compass as you turn, stop when that needle has moved 90 degrees from north. Holding the base plate firmly, turn the dial so the N once again lines up with the direction-of-travel arrow. That number should be a 90-degree difference from the first bearing determined in step 4.
A back bearing is the opposite direction from which you just traveled. Numerically, it is 180 degrees from your forward bearing. If your forward bearing is between one and 179 degrees, you would add 180 to find your back bearing. If your forward bearing is between 181 and 360, you would subtract 180 degrees. For example, if you are heading at 25 degrees, 25 + 180 = 205 degrees. Your back bearing is 205 degrees. Once you have memorized the eight major points on the compass, you would know that 205 degrees is a south westward direction. If you were heading at 300 degrees, your back bearing would be 300 – 120 degrees. Again, you would know that this is an east to southeast direction. If you would add the 180 by mistake, your number would be larger than the number of bearings on a compass dial. Back bearings are useful to know when you are setting up a transect and the vegetation is too high to see the other side of the wetland. You may have to travel around the wetland and take a back bearing to line up with the beginning of your transect before you finish flagging the line.
A few warnings about using a compass:
- Compasses read from magnetic north, not true north. The difference in degrees between magnetic north and true north is called declination. Declination varies with location, topography and other factors. For example, if the declination is six degrees east of true north, this means the compass needle is pulled six degrees to the east. Therefore, magnetic north is six degrees to the east of true north. To compensate, move the compass base so that is subtracts six degrees.
- Be sure your belt buckle isn’t metal. If it is, the buckle might affect the magnetic end of the needle, making it point to you instead of north!
- A knife in your pocket, metal snaps on your clothing, a whistle hanging around your neck or any other nearby metal object also will disturb the magnetic end of the needle.
To use a map and compass together:
- Using your compass, position the map so that it reflects the directional orientation of the area. To do this, place the map on a flat surface; set the direction-of-travel arrow on N; place the compass parallel to one of the side margins of the map; hold the map and compass steady and rotate both until the needle comes to a stop on the declination mark (the masking tape). Your map is now lined up with true north. Keep the map in that position.
- Locate on the map where you are currently (baseline transect) and where you wish to go. The teacher will assign this.
- Using the edge of your compass or some other straight edge, mark a line on the map between where you are to where you want to go (direction of travel).
- Lay the compass along the straight line and rotate the housing until the needle points to the direction of travel.
- Now read the bearing at the direction-of-travel arrow and walk in that direction.
- Line up trees (or other recognizable objects) ahead of you and head for the first one. Then line up a third object with your second object and head for the second object. Keep doing this until you reach your destination.
- Upon reaching your destination, you will find an object your teacher has placed there for you to collect. After you have collected your object, return to the starting point and give your teacher what you have collected.
- Using a large map of the area studied (drawn on a plastic table cloth or something similar), mark the beginning point and have each person or group show where they collected their item.
- Short creative reading: “Let me tell you how to use a compass.”
Continue compass reading back at school (school campus, a park, a nature area).
- Reading from land to map, plot your travel direction on a map.
- Why should one hold a compass level and with the line of travel arrow pointing away from the person?
- What problems did you have reading your compass or topography map?
- How do you determine your back bearing using a compass bearing?
- Why is it important to always take a compass reading before going into the woods or hiking?
Handbook for Wetlands Conservation and Sustainability, “How to Use Compass,” Izaak Walton League of America; 1996; pages 181-183.
Back bearing – bearing along the reverse direction of a line, especially in compass use
Compass bearing – direction measured from one position to another using geographical or celestial reference lines; also direction relative to north as indicated by a compass
Declination – angular difference between true north and magnetic north; also the difference in degrees between magnetic north (the direction the magnetic needle on a compass points) and true or geographic north (the direction maps are printed toward)
Pace – step made in walking, usually 30 inches
Topographic map – graphic representation showing natural and/or physical features of a landscape, including altitude contours; also called contour map
Topography – graphic details on maps or charts of a region’s natural and man-made features that shows relative positions and elevations