The shortest distance between two points is a straight line. However, a straight line is generally not the best route of travel between two points.
Selection of a route begins with a thorough map reconnaissance. Some questions you might ask as you select potential routes are: What lies between points A and B in terms of terrain? What are the obstacles- a stream, lake, high peak, steep slope? These obstacles should be avoided. What does the route look like in terms of elevation gain or loss? When you do your map study, imagine what the terrain is like from its map representation and ask yourself if you want to be walking through, up, down, or over it.
Generally speaking, the best route is one that maintains a consistent elevation, avoids low points and valleys (there is potential for moisture and dense vegetation), and avoids all water obstacles. Also, if a gain in elevation is part of your route, try to spread the climbing over as much distance as possible. It is easier to gain 1000 feet in elevation over 5 miles than it is in just one mile. The same is true in terms of using distance for elevation loss.
For more on Map Reconnaissance, see my Blog post of 12 February, 2009.
Terrain association is a method of navigation. It replaces using the compass to calculate an azimuth for direction of travel, but it does not make the knowledge of using a compass any less important. Terrain association is more useful in certain terrain- it works well in the desert southwest, it is less desirable for use in the swamps of the southeast on a dark and rainy night.
To successfully use terrain association as a method of navigation, you must first study and become familiar with basic terrain features, map colors, water features, man made features and most importantly contour lines- you must know how to read a map. When you become proficient in your knowledge of terrain features and other map features and their map representations you can move faster and with more accuracy.
To use terrain association to navigate, begin by studying the map and ground carefully before you start walking. Study your route of march and note prominent terrain features that are visible and those that you will see after walking a kilometer or two. Note where you may encounter a stream, a prominent hilltop or a road. As you move along your route of travel you should constantly be orienting yourself on the ground with that terrain on your map. The map representation and what you see should match! This is terrain association.
Frequent map checks are important to maintain constant knowledge of your location. By comparing your position in relation to terrain features and other map features you are checking your map as you move. Using terrain association to navigate, you will always know your location and minimize the possibility of becoming lost.
Assigning checkpoints along your route allows you verify your position positively as you move. Checkpoints should be easily identifiable terrain features and may include the following: a hilltop, road intersection, cliff face, or stream junction. Be careful when selecting your checkpoints- they should be major features! Remember that features do not always look the same on the ground as they do on the map. Avoid intermittent streams, they may not be identifiable during the dry season. Avoid using manmade features when possible- a cabin may have long since disappeared from where it once stood. Remember to use your pace count for measuring distance between points. Keeping track of distance traveled is key in accurately moving between checkpoints.
This technique is also known as line of sight travel. It is simple, useful when speed is essential, but lacks accuracy. This method works better in more open areas where visibility of points is greater. To use this method, locate your start point and you objective point. Measure the map distance between the two points and calculate the magnetic azimuth. Set the azimuth on your compass and head in that direction. You can use checkpoints with this technique, or use this technique in conjunction with traveling in legs, adding accuracy, as described below. Be sure to keep a pace count as you travel.
Travelling in Legs
Travelling in legs resembles travelling using checkpoints. However, instead of using checkpoints for verification during travel, when breaking up your trip into legs you actually set your azimuth for each of the intermediate points. There may be many offsets in this type of travel. Rather than staying on a general course, as in dead reckoning, the route is broken up into distinct distances and azimuths, which, being shorter, allow for more accuracy in navigation. For example, instead of moving from point A to point B, your are adding points C, D, and E in between your start and end points.
You should try to limit the distances you travel on each azimuth to roughly 300 meters. You are more likely to arrive at your destination moving in three – 200 meter legs than if you traveled 600 meters straight on one azimuth.
This technique is also know as planned deviation. We all have a natural tendency to deviate form a straight line while navigating. Causes for this include following the natural lines of drift in the terrain and favoring one side of our body, right or left, and thus moving in that direction.
We can use this to our advantage during navigation. Instead of moving to our objective point and then trying to guess if we are to its left or right, a common occurrence, we can deliberately adjust to our left or right before beginning travel. This ensures we know which direction we have to move, left or right, when we have traveled the proper distance to our objective.
Two simple methods are used for deliberate offset. First you may add 5 or 10 degrees to your azimuth, depending on how far off your objective you want to be, and your level of confidence. Remember that the distance you are traveling to your objective directly relates to how far off your objective you will arrive. For every 1 degree of offset and 1000 meters of travel you will be off by approximately 18 meters. For example, if you add 10 degrees to your azimuth and travel 500 meters you will be off by approximately 90 meters.
The second method is to simply favor one side or the other as you move over the ground. If you are right handed you will most likely favor your right side. Experience shows that our handing is the direction we tend to favor. You can enhance this tendency by deliberately passing obstacles on the right side. If you come to a tree or grouping of brush in your path, simple move around it to your right. Continue moving to the right of all obstacles and when you have traveled your desired distance you should be to the right of your objective point.
This method is obviously not as accurate as the first. However, over time you will become familiar with your own tendencies and more comfortable with trusting this simple method.
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