Navigate with Compass and Map

Navigate:

The act or task of moving through a place or along a route, to make one’s way over or through : traverse Navigate.1

To be able to navigate you first need to be able to read a topographic (topo) map. Being able to read a topo map does not take any special skills. Once you learn the nuances of maps, reading them becomes second nature. Being able to decipher the lines and squiggles that make up your map brings trip planning to a whole new level. Being able to recognize features on a map and find them in the field reinforces your confidence in knowing your location all of which aids your ability to navigate. Features as described below augment the cartography and help describe the landscape making it easy to navigate.

Reading and understanding the map is only one part of navigation. Using a compass along with the map is essential to being able to navigate to where you want to go. With today’s technology there are many electronic medium that can enhance your ability to navigate and route find, but these should never replace your map and compass or your skill to use them. Batteries die, electronics fail. Unless you loose your map and compass you have the tools to stay found and navigate to your destination.

Map Symbols and Colors help you Navigate
Red: is over printed to highlight primary and secondary roads; it also designates surveying features associated with public land surveys. 
Range Line Township or Range Line Land Grant Boundary Land Grant or Mining Claim
Range Line Fence Line Route Marker Route Markers
Black: represents man-made features.
Divided Highway Divided Highway Primary Highway Primary Highway
Secondary Highway Secondary Highway Light Duty Road Light Duty Road
Unimproved Road Unimproved Road (Dirt/Gravel) Trail Trail
Multi-Track Railroad Railroad – Multiple Tracks Single Track Railroad Railroad – Single Track
Bridge Bridge Drawbridge Drawbridge
Foot Bridge Footbridge Tunnel Tunnel
Overpass - Underpass Overpass – Underpass
Dwelling
Dwelling
School School Church Church
Airport Airport Landmark Point Landmark
Campground Campground Picnic Area Picnic Area
Cemetery Cemetery: Small / Large Powerlines Power Lines
National Boundary National Boundary State Boundary State Boundary
City Boundary City Boundary National Park Boundary National Park or Forest Boundary
Quarry Quarry / Open Pit Mine Cave Cave or Mine Entrance
Landmark Landmark Line (Labeled as to Type) Windmill Windmill
Blue: represents water features.
Lake Lake Glacier Glacier Contour Lines
Stream Stream River River
Intermittent Stream Intermittent Stream Disappearing Stream Disappearing Stream
Small Falls Small Falls Small Rapids Small Rapids
Large Falls Large Falls Large Rapids Large Rapids
Dam with Lock Dam with Lock Canal With Lock Canal with Lock
Large Dam Large Dam Small Dam Small Dam: Masonry, Earth
Water Well Water Well Spring Spring
Swamp Marsh or Swamp
Brown: represents contour lines and elevation markers.
Index Contour Line Index Contour Lines Intermediate Countour Line Intermediate Contour Lines
Supplementary Contour Line Supplementary Contour Lines Depression Depression Contour
Road Fork with Elevation Road Fork Sector Corner with Elevation
Green: represents vegetation features
Woods Woods Orchard Orchard
Scrub Vegitation Scrub Spare Vegitation Sparse
Purple: revisions made by areal photography.
Landmark, Camp, Dwelling Landmark, Campground, Dwelling

Reading Topographical Maps to help Navigate

Understanding what a map is trying to tell you will help you navigate the terrain. The thin brown lines that twist around your topographical map are called contour lines. Each contour line represents a known equal elevation. If you were to navigate along a contour line, you would neither climb nor descend and if you follow it around long enough you would end up where you started. Furthermore depending on the scale of the map, contour intervals will vary. On 7.5-minute quadrangle the scale is 1:24,000 (1 inch equals 24,000 inches) and intervals are 40 feet apart unless otherwise noted.

Map Interpretation

Interpreting a topographical map requires a little imagination. Therefore, when looking at a map you are peering down on the terrain from above. You must translate those lines and squiggles into ridges and valleys. If you look at the image on the left (Fig. 1), you can imagine a small building sitting next to a little hill (figure 2 and fig. 3).

3D View

Fig. 1

Side view

Figure 2

Overhead Topo View

Fig. 3

Valleys and Ridges

Figure 4

Contour Lines

Also, the spacing between lines is very important. The wider the space between the lines, the gentler the slope. The closer the contour lines are spaced the steeper the slope. Where contour lines intersect  they result in a cliff. Look at the contour lines on Mount Whitney – Keeler Needle Quadrangle (Figure 4). The contour lines on east side are very steep, but to the west side is less steep. Whether traveling cross-country or on a trail being able to read a map can help determine if you will navigate in open, flat terrain, or steep incline. This is especially important when you navigate cross-country. You would want to navigate around cliffs and try to avoid steep terrain.

Ridges and Valleys

Keys to reading topographical maps are the V’s and U’s made by the contour lines. V’s and U’s represent valleys and ridges. The easiest way to differentiate between the two is to see which way the V’s or U’s point. When the bases of the V’s or U’s are pointing up hill you are looking at a valley, similarly if the V’s or U’s are pointing downhill they depict a ridge. In Figure 4, the V’s between Mount Whitney and Keeler Needle point up hill representing a valley or couloir. The V’s pointing off the right side of the figure below Keeler Needle are pointing downhill, this is a ridge.

Ridges, Valleys, and Passes

Figure 5

To help determine between ridges and valleys is that valleys have rivers or streams, but not always. Knowing that if V’s pointing downhill represents ridges and U’s pointing up hill represents valleys helps identify passes where they meet. As depicted in Figure 5 the V’s that point downhill from peak x8515 meet the V’s from the other direction forming a pass. The U’s with their bases going uphill shows the terrain descending north and south from the pass. The dashed line (trail) that approaches the pass from the north traverses the base of a steep wall (close contours) above a glacier (blue contours). In this instant, the Ptarmigan Tunnel cuts through the pass and then the trail switchbacks and descends into the valley to the south.

Declination

Declination is also an important feature to note when reading topographical maps. Without allowing for declination, when you navigate with your compass you could find yourself off course. In the lower left hand corner of most maps, you will see a V. This V shows the difference between true north, magnetic north. All features on the maps are drawn to true north. If you ignore the declination information, in this example, and just follow the red 

Declination

Figure 6

needle in your compass you would end up 20½° (figure 6) off course. Depending on how far you are navigating you may miss your objective altogether.

Depending on where you are in the world, declination is either east or west. In figure 6, the declination is 20½° east. The magnetic north (MN) is east of true north in this example. With east declination, to find your true course subtract 20½° from the track. An easy memory aid is “East is least, west is best”. Subtract East declinations and add West declinations to change from true to magnetic.

Cross-Country Travel

Another important note about declination is that it changes. Before you try to navigate, especially cross-country make sure that your map is up to date. For example in Montana the declination in 1968 was 20 1/2 degrees east, new maps with an updated 2011 declination for the same area is only 14.6 degrees east. Over short distances, you may not notice this 6 degree error But if you had to navigate several miles you could miss your destination by a significant distance. One way to make sure you make your destination is by using and intentional offset described later.

Compass Anatomy

Compass Anatomy

Figure 7

Before illustrating the application of declination with a real world example, let view the anatomy of a simple compass (Figure 7). Most compasses have a see thru or transparent base so you can see the map beneath the compass. Index lined to help line the compass alone routes or orientation lines on maps. The rotating bezel allows the alignment of the meridian lines to either true of magnetic north reference lines. The magnetic needle points north and use the ruler to measure distances.

declination

Figure 8

To help illustrate the problem of declination while you try to navigate, look at figure 8. You are planning to hike cross-country across Granite Park from altitude mark 6050 on the Highline Trail to the Chalet. Opening up the map, mark the route. Using a compass, compute the direction from point 6050 to the Chalet. To do this place the side of the compass along the drawn route, rotate the bezel of the compass until it points to the top of the map and the meridian lines are parallel with north reference lines. On the plate of the compass, in the center, extending from the bezel is an arrow. Read the direction off the bezel, 320° opposite the arrow. Knowing that the declination in this area is 20½° east, when leaving point 6050, the correct course would be 300°. (320° – 20° = 300°)

Triangulation

The other time declination comes into play is trying to triangulate your exact

Triangulation

Figure 9

location with the surrounding terrain and your map and compass. The art of pin pointing your position relies on the knowledge of declination. Somewhere on the Highline trail, holding the compass pointing towards Ahern Peak rotate the bezel until north is in line with the magnetic arrow and read the heading to Ahern Peak. 330°. Do the same with Ahern Pass. 60°.

Knowing that the declination is 20 ½° east and the readings just taken are magnetic; they must be changed into true bearings. 330° +20° = 350° and 60° + 20° = 80°. The process is the opposite of true to magnetic. Instead of subtracting for east and adding for west, add for east and subtract for west. With the compass, rotate the bezel until the arrow on the base lines up with 350°. Place the compass with the edge on Ahern Peak and rotate the compass around until the north arrow on the bezel is parallel with the side of the map or north reference lines. Draw a line along the edge of the compass. Once this is done rotate the bezel of the compass until 80° is aligned with the arrow on the base and go through the same process from Ahern Pass. (See red line in figure 9). Where the two lines intercept is your location. If the declination was ignored (see magenta line in figure 9) you would triangulate your position incorrectly and come to the conclusion that the map was incorrect because the trail you are standing on looks like it should be drawn further south on the map.

Navigate Technique

Intentional Offset

Figure 10

When you want to navigate to a certain point a good technique is to use an intentional offset. First of all determine what direction your destination is. Next, you offset an error to one direction or the other. Looking at Figure 10 for example, you are at the end of the 4-wheel drive track and want to travel to Burnt Springs. Calculating your direction to navigate (magenta arrow) you calculate a heading of 235 degrees. If you navigate on a heading of 245 degrees, an offset to the right 10 degrees when you reach the ravine you will be north of the spring. Turn left and follow the ravine south to the spring. If you navigate on the 235 heading and drift south a little you could pass the spring without knowing until you come to the dirt road. Now you would have to triangulate your position and navigate to the spring from this new location.

Trip Planning

Finally, when you are planning your trip and studying your route you can estimate how long it will take to navigate your planned route. The average pace of a hiker with a full pack is 2 to 3 miles an hour, If you are climbing or descending it will take you longer than if on level ground.

Therefore, let say we are planning a hike from Longs Peak Ranger Station to The Boulder Field (Figure 11). Looking at this route (marked in magenta) measure the distance that you will travel, then at various high and low points along your route.

Planned Route

Figure 11

Using a piece of string trace your route then compare its length with the scale on the bottom of the map. We computed 5.6 miles. Next since this route is all uphill, we just need our starting elevation 9360 and our finishing elevation 12720. To find these two altitudes we notice that the heavy contour line near the ranger station is 9400 feet. The parking lot appears to be one contour line less; the chart says each contour is 40 feet. 9400 – 40 = 9360. The same method is used for the boulder field. The heavy contour line is 12800 feet. The DEST is two contour lines less, 12800 – 80 = 12720.

Trip Estimation formula

The total altitude gain is 3360 feet (12720 – 9360 = 3360). To compute your time take your total distance (TD) by your average miles per hour (MPH) that you travel on level ground. Add to this your total altitude gain (AG) divided by 500 and multiply by 65%, if there is downhill travel take your total altitude loss (AL) and divide it by 1000 and multiply that by 35%. Your formula looks like this: TD/MPH + (AG/500 * .65) + AL/1000 * .35) = hours

Therefore armed with this information we can compute how long our day will be. 5.6miles/3 mph = 1.8667 hours (3360/500 * .65) = 4.368 hours. There isn’t any significant altitude loss on the route so we just add these two times together. 1.8667 + 4.368 = 6.2347 rounding the number to two decimal places computes our estimated time to navigate this trail at 6.25 hours. Furthermore you need to remember this is just an estimate to give you an idea how long the hike will take.

by John Dragotto

Footnotes

  1. ” Merriam-Webster.com. Merriam-Webster, n.d. Web. 3 Nov. 2018.