Map Reading & Compass Use

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Samuel Gilbert
6 years ago
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1 Spring 2013

2 Kestrel Land Trust Page 2 / 10 Contents Map Basics... 3 Map Types... 3 Terrain Association... 4 Estimating Distance: Pacing... 4 Contour Lines... 5 Navigating with a Compass... 6 Compass Types... 6 Parts of a Compass... 6 North and Declination... 7 Taking a Bearing from a Map... 8 Following or Taking a Bearing in the Field... 9 Appendix: Reading a Survey Map Contact Kestrel Land Trust Office: 233 North Pleasant St. #42, Amherst, MA Mail: PO Box 1016, Amherst, MA Chris Volonte Stewardship Manager (office) (cell) chris@kestreltrust.org

Kestrel Land Trust Page 3 / 10 Map Basics You will use three main types of maps: Topographic Maps Show: Land forms, elevations Water bodies, rivers, streams Roads,

Water bodies, rivers, streams Roads, structures Unique feature: Detailed photogr

3 Kestrel Land Trust Page 3 / 10 Map Basics You will use three main types of maps: Topographic Maps Show: Land forms, elevations Water bodies, rivers, streams Roads, structures Unique feature: Contour lines (see page 5) Disadvantage: Forest cover type and other details not shown Aerial Maps Show: Forests, fields, other land uses Water bodies, rivers, streams Roads, structures Unique feature: Detailed photographs show forest cover types and readily recognizable features (e.g., structures, power line cuts, vernal pools, wetlands, rock walls, open ridges) Disadvantage: Difficult to detect elevation changes Survey Maps Show: Property boundaries (best accuracy) Boundary markers (e.g., iron pipe, rebar, stone monument, drill hole) Unmarked points (no pin) Roads, structures Woods roads, stone walls, barbed wire, wells Water courses, wetlands, ledges, tree lines Unique feature: Compass bearings (see page 6) Disadvantages: Difficult to detect elevation changes, forest cover and vegetation types

4 Kestrel Land Trust Page 4 / 10 Map Basics Terrain Association You can use all three types of map together to orient yourself on the ground: Topographical Features Contour lines reveal basic land forms (e.g., hilltop, valley, ridge, depression, saddle) that should match up with what you see on the ground. Vegetation Aerial maps reveal differing vegetation types (e.g., areas of coniferous versus deciduous forest, beaver ponds and other wetland areas, vernal pools, open fields, hedgerows, shelterbelts) and open areas (e.g., clearings, power line cuts, exposed bedrock). Hydrography Topographical maps and aerial maps both show the shape, size and locations of lakes, ponds, and streams. Topographic maps indicate the direction streams are flowing (see page 5). Human-Made Features All three map types show buildings, roads, bridges, high-tension lines, etc. Aerial maps can often show rock walls and other details. Survey maps show details such as wells, barbed wire fencing, rock walls, boundary markers, woods roads, etc. Estimating Distance: Pacing Pacing is a simple way to estimate the distance you have traveled. All you have to do is pay attention to the number of steps you have taken from your starting point. 1 pace = 2 steps Count each time you put down your right foot (or left, if you prefer, but be consistent!) Typical pace = approximately 5 feet (good estimation) EXAMPLE: 25 paces = 5x25 = 125 feet Note: On level, open ground, pacing can be fairly accurate with practice. But on slopes and in brushy or rocky areas, its accuracy diminishes. In difficult terrain, allow for the inevitable shortening of your pace (downhill as well as uphill).

Contour interval the distance between contour lines (typically given in feet). The contour interval in the map at right is 20 feet. Spot elevations heights of identifiable features (e.g., mountain summits).

5 Kestrel Land Trust Page 5 / 10 Contour Lines Contour lines indicate the elevation above sea level of land features. The illustration here shows how land features are rendered by contour lines in a topographic map. Index contours contour lines labeled with the elevation (typically every fifth line). Contour interval the distance between contour lines (typically given in feet). The contour interval in the map at right is 20 feet. Spot elevations heights of identifiable features (e.g., mountain summits). E.g., see the ridge top labeled 275 above. Depression small dip in the landscape. Circles with hatch lines indicate a depression, pit, or sinkhole. Summit indicated by concentric loop shapes. Saddle a ridge between two hills or summits, generally indicated when two loop shapes are enclosed in a larger, open 8 shape. Rugged terrain Jagged, rough contours indicate large outcrops of rocks, cliffs, and fractured areas. Tightly spaced contour lines intersecting your direction of travel mean a steep climb or drop. V shapes indicate stream beds and narrow valleys. The point of the V points uphill or upstream. M shape contours point upstream from stream junctions. U shapes indicate ridges with the curve of the U pointing downhill.

Kestrel Land Trust Page 6 / 10 Navigating with a Compass Cardinal directions: North 0 / 360 East 45 South 180 West 270 Two compass types: Azimuth (pictured top right) 0 to 360 All bearings count from

g., southwest is S 45 W). Notes Most survey maps use quadrant bearings. When using surveys, disregard minutes and seconds given in the bearings.

6 Kestrel Land Trust Page 6 / 10 Navigating with a Compass Cardinal directions: North 0 / 360 East 45 South 180 West 270 Two compass types: Azimuth (pictured top right) 0 to 360 All bearings count from zero, measuring clockwise from north (e.g., southwest is 225 ) Quadrant (pictured below right) 90 intervals (measured from north or south) Direction is specified as number of degrees east or west of either N or S (e.g., southwest is S 45 W). Notes Most survey maps use quadrant bearings. When using surveys, disregard minutes and seconds given in the bearings. Quadrant bearings can be converted to azimuth bearings and vice versa: S 45 W equals 180 plus 45 = 225 S 30 E would equal 180 minus 30 = 150. Key components of a compass: Needle The arrow (usually a red end) points to magnetic north. Housing (Dial) A movable circular dial with degrees marked on the outer edge. Each mark represents 2 degrees. Orienting Arrow An arrow-shaped outline within the housing (labeled here as Compass dial arrow ). This arrow will point north unless your compass is adjusted for declination. To follow a bearing, position the compass needle within this arrow (see page 9). Base Plate This is the part of the compass you hold in your hand. The front of the base plate has a direction of travel indicator (labeled here as Direction of travel arrow ). A compass with a sighting mirror will also have a direction of travel indicator at the top of the mirror.

7 Kestrel Land Trust Page 7 / 10 Navigating with a Compass Be aware of the different norths True north (star) a line from any point on the earth s surface to the geographic north pole. All lines of longitude are true north lines; they converge at a single point. It is common practice for maps to be oriented with true north at the top. Magnetic north (MN) the direction a compass points toward the magnetic north pole. Magnetic north is not a constant it varies depending on your geographic location (see illustration below). It also varies (slowly) over time. The difference between true north and magnetic north can be sufficient to take you well off course in the field (see Declination, below). Grid north (GN) a vertical line on a map that runs parallel to the prime meridian. Grid north lines do not converge at a single point. On a flat map, grid north lines do not follow true north lines, as true north follows the Earth's curved surface. For our purposes, the difference between true north and grid north is insignificant. Declination Declination is the difference between true north and magnetic north. Currently in our region, declination is approximately 14 west. To compensate for declination when you read a bearing off a map in our area, ADD 14 to the bearing. ( Declination west, compass best = add) You don t need to worry about declination if (1) your map uses magnetic north (surveyor s maps sometimes do), or (2) your compass is already set to account for declination and your map uses true north (most maps do). To adjust your compass for declination, rotate the compass housing with a screw and/or key provided with the compass. To adjust for west declination, rotate the orienting arrow counter-clockwise from 0 the number of degrees of declination (in our case, 14 ). The orienting arrow points to 346.

Kestrel Land Trust Page 8 / 10 Navigating with a Compass How to Take a Compass Bearing from a Map Draw a straight line from your starting point over to the map edge in the

Turn the housing (dial) until the orienting arrow points N on the map (either aligned with map edge, or aligned with the north indicator on the map).

8 Kestrel Land Trust Page 8 / 10 Navigating with a Compass How to Take a Compass Bearing from a Map Draw a straight line from your starting point over to the map edge in the direction you want to travel. Place the base plate of your compass (right or left edge) along this line. Turn the housing (dial) until the orienting arrow points N on the map (either aligned with map edge, or aligned with the north indicator on the map). Ignore the floating needle; focus only on the orienting arrow within the housing. Read the bearing and record it. Note: If your compass is not adjusted for declination and your map is oriented on true or grid north, add 14 to the bearing. Orienting arrow points N Ignore floating needle

Kestrel Land Trust Page 9 / 10 Navigating with a Compass How to Follow a Bearing EXAMPLE: 330 (azimuth compass) To set your bearing, turn the housing (dial) until 330 lines up with the direction of

The direction of travel indicator should point straight ahead in front of you.

9 Kestrel Land Trust Page 9 / 10 Navigating with a Compass How to Follow a Bearing EXAMPLE: 330 (azimuth compass) To set your bearing, turn the housing (dial) until 330 lines up with the direction of travel indicator on the compass base (see illustration, right). Hold the compass level in front of you approximately waist high (brace your elbows against your ribs to steady them). The direction of travel indicator should point straight ahead in front of you. Holding the compass steady and watching the dial, rotate your body until the compass needle is positioned within the orienting arrow outline. (see illustration, right). The red end of the needle should be at the pointing end of the orienting arrow. (This is known as putting red in the shed. ) Now you are facing the correct direction to travel. Look up and sight an object such as a tree or fencepost in that direction (the farther, the better). Then forget the compass temporarily and walk to that object. Remember to count paces if you need to (see page 4). When you arrive at your sighting object, repeat the process and pick out a new object to sight. Repeat until you reach your destination. How to Take a Bearing Bearing set to desired direction of travel Needle positioned within orienting arrow Face the point you want to determine. Hold the compass level in front of you approximately waist high (brace your elbows against your ribs to steady them). The direction of travel indicator should point straight ahead in front of you. Note: If you are using a compass with a sighting mirror your bearing will be more accurate if you hold the compass at eye level and use the mirror to read the dial. Keeping the direction of travel indicator pointed at your target, turn the dial until the compass needle is positioned within the orienting arrow outline. The red end of the needle should be at the pointing end of the orienting arrow. (This is known as putting red in the shed. ) Read the bearing at the direction of travel indicator. This will be the magnetic bearing if your compass is not adjusted for declination; it will be the true north bearing if your compass is adjusted for declination. Note: Compass readings are affected by the presence of iron and steel objects, including pocket knives, belt buckles, railroad tracks, trucks, electrical lines, etc.

Using Map and Compass Together

Using Map and Compass Together In situations where you foresee a potential evacuation on foot, where there are no roads, and no indication as to the direction of travel (i.e., road signs), it is recommended