I wanted to spend some time refreshing my knowledge of a compass and learning further about orienteering. I did so recently in the context of reading The Wilderness Route Finder by Calvin Rustrum. Published in 1967, Rustrum explains in detail numerous ways of determining one’s position in the wilderness at a time before the use of GPS. While the book also details navigation by sextant, radio signals, and others, I was most interested in the portions of the book related to use of the compass and general way finding.Calvin Rustrum is one of my favorite authors on the topic of the outdoors. Rustrum was an American author who lived and traveled the wilderness of North America through the 20th century. Outdoor travel and living changed significantly during this time period as technology, much of it developed and used for the world wars, was adopted. Furthermore, the 20th century saw the rise of outdoor travel and living for recreation. Rustrum wrote fifteen books. While some are stores of his travels and commentary about environmentalism and modernity, some of his best works are his practical guides of wilderness skills that effectively blend context from his experiences with valuable traditional skills and incorporation of the technologies developed during his lifetime.
Rustrum begins by explaining the various reasons why we can become disoriented or lost. Even with a map, without the proper skills to locate one’s self on that map the map is of little value. “This job of equating map and natural factors is the only map reading that can have any practical, functional value where route finding is concerned,” says Rustrum.
A compass is a relatively basic instrument, there is a magnetic needle and a declinated compass housing. For orienteering purposes, there is an orienteering arrow inside the compass housing, a direction of travel arrow, and the compass housing is rotatable.
Fig. 1 – A basic orienteering compass
The orienteering arrow is used to orient the compass to magnetic north by aligning the magnetic needle with the orienteering arrow. The direction-of-travel arrow is used to point at the object of reference or desired direction of travel.
Fig. 2 – Orienteering arrow aligned with magnetic needle, the direction-of-travel arrow indicates a ___ degree bearing.
The magnetic needle of the compass aligns to the natural magnetic fields of the earth. These can vary substantially based upon geography and position around the globe. Without knowledge of this phenomenon and the ability to correct for it, Rustrum says, “it is evident then that in no sense can we consider the needle to be pointing at anything.” However, for most travel or orienteering, the travel is so localized (even within a wilderness area) that once accounted for, change in magnetic declination need not be further considered.
A general knowledge of the magnetic declination for an area in which you will be traveling is needed. This general knowledge is used to account for the error between where the magnetic needle will point and the direction of true north. Maps are available for these purposes. A map of magnetic declination and further information can for example be found at https://education.usgs.gov/lessons/compass.html. These maps have an Agonic line (or lines) where the compass needle points to True North and Isogonic lines that map locations of the same declination correction (either East or West) that must me applied. I am lucky in that the Agonic line extends through both Western Wisconsin and the Boundary Waters, two places that I have frequented and hope to return to. In fact most anywhere in Wisconsin is within a degree or two from True North.
So we’ve now identified how a compass works, and how to correct for the natural error in As observed by Rustrum, “We have no innate sense of direction, and for this reason, in order to maintain a systematic orientation we must always relate ourselves to something else.” In route finding, this something else is a “line of position.” By determining one or more lines of position, one’s place relative to a map can be identified, and one’s movement directed and evaluated.
The line of position can take three general forms: 1) a base line; 2) a bearing or direction of travel; and 3) a triangulation line. Effective way finding typically uses two or more of these lines of position. Geometry teaches us that a point is an intersection between two lines. Therefore, if we want to identify our location, we likely want to define it with two intersecting lines of position.
A base line is most typically a physical feature that is identifiable on a map. The base line can can be a river, a shore line, a road, a railroad, or other lengthy feature. The base line serves as a reference and typically as a bound when traveling between two locations. While the base line is useful, without an intersecting line, one does not know where along the base line one is located. As an example, you are camping along the shore of a large lake, you travel inland and then turn around to return to camp, you reach the shore of the lake again, but cannot see your camp. Without more information, you do not know which direction along the shore you need to travel to return to the camp. In another example of a base line, an artificial base line can be created when there is a prominent feature which can be used as a reference. As an example, a prominent peak is visible on the horizon. The peak is at a bearing of 300 degrees from your campsite. That creates a referential line base line.
A bearing or direction-of-travel line is the basic definition of an intended direction to a destination. When one’s location and destination location are known, the bearing is a matter of following the determined direction from the compass. However, the ideal bearing is often interrupted by physical features for example, rocks, bogs, trees, or ravines. Deviation from the ideal bearing is common. As these deviations are made, they must be noted and accommodated for, in what amounts to a navigational zig-zag across the ideal bearing. Frequently an estimation of the distance traveled either with use of a pedometer or a recorded time of travel estimation can help to give you an idea of the accommodation needed to return to the ideal bearing line.
To continue the example from above, you now leave your campsite along that the 300 degree bearing between your campsite and the peak. Later you leave that bearing to explore a region north of the bearing line. When it is time to return to camp, you can first return on a south-western bearing (230 degrees) until the the peak is again at a 300 degree bearing, then return along your base line to camp.
Thus effective navigation may use a combination of boundary lines and bearing lines, the boundary line giving certainty of position (somewhere along the boundary line), but not of direction, while the bearing line gives certainty of direction, but not of position.
The last type of line of position is a triangulation line. As noted above, any point can be identified by the intersection of two lines. If two physical landmarks can be found, a bearing to each of the landmarks can be taken. By drawing these bearing lines out on a map, one’s position can be identified on the map. If more certainty is desired, more than two landmarks can be used so that an error in identifying one of the landmarks can be deduced. More importantly than as a tool for locating one’s current position, triangulation can be used to identify and record locations for others to find the same location.
My summary has only scratched the surface of what Rustrum details in his book, including with more details, examples, and pictures than what I’ve provided here. I appreciated reading the Wilderness Route Finder as a way to reflect more deeply about using a compass and navigation more generally. While I’ve focused on the parts applicable to navigation with a compass, I found the discussion of other tools to be interesting as well, particularly the sextant. I recommend this book to anyone who is interested in learning more about navigation and the use of many different navigational tools.