Kindle Notes & Highlights
by
Bob Burns
Read between
August 9 - November 18, 2019
Flat areas: No contour lines at all. Gentle slopes: Widely spaced contour lines. Steep slopes: Closely spaced contour lines. Cliffs: Contour lines extremely close together or even touching. Valleys, ravines, gullies, and couloirs: Contour lines in a pattern of Us for gentle, rounded valleys or gullies; Vs for sharp valleys and gullies. The Us and Vs point uphill, in the direction of higher elevation. Ridges or spurs: Contour lines in a pattern of Us for gentle, rounded ridges; Vs for sharp ridges. The Us and Vs point downhill, in the direction of lower elevation. Peaks or summits: A concentric
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If you ever forget whether upward-pointing or downward-pointing contour lines indicate ridges or gullies, just remember that streams usually flow down gullies, and not on ridges. So if you have a map of a hilly or mountainous area, find a thin blue line indicating a stream, and examine the contour lines around it. The upward-pointing contour lines will remind you that they indicate a gully.
The margin also gives the area’s magnetic declination at the time the map was last updated, which is the difference between true north and magnetic north.
Some maps have a grid of UTM (Universal Transverse Mercator) lines printed on the map, and these can be used as north–south reference lines. North is usually at the top of the map, unless otherwise indicated.
the offset of the UTM grid is more than 1°, then you should use surveyors’ section lines (usually printed in red). If the map has no section lines, or if the section lines do not truly run north–south, you can draw in your own north–south lines, as follows:
there are faint (usually blue) UTM “tick” marks along the edges of such maps showing the locations of the 1000-meter lines
However, if the amount of difference between true north and grid north is greater than 1°, then you should draw in your own north–south lines parallel with the edges of the map,
Using the direction of the slope cannot prove that you are at any particular place, but it can disprove it, and this can sometimes be a big help in trying to figure out where you are.
The map will not show all the terrain features that you actually see on your trip, because there is a limit to what mapmakers can cram onto the map without reducing it to an unreadable clutter. If a feature is not at least as high as the contour interval, it may not be shown,
Check the date of the map, because topographic maps may not be revised very often, and information on forests and on roads and other works of the human hand or natural disaster (such as the eruption of a volcano) could be out of date.
TIP: When you learn of changes (such as road or trail closures), you should note them on your map in pencil, along with the date.
One of the most important aspects of carrying a map is to do so in such a way that you can get to it at any time. We suggest that you carry it in your pocket.
It is best to fold your map so that your entire route for a given leg of the trip will always be visible without unfolding the map, if possible.
TIP: Try to keep folds away from key route junctions or other important areas of interest, since folds tend to degrade with time and wear, particularly if the map gets wet.
We recommend against laminating maps for your wilderness adventure, since doing so makes it difficult to fold or write on the map.
Most compasses have a lanyard—a piece of cord a foot (30 cm) or a little longer for attaching the compass to your belt, jacket, or pack. It is not a good idea to put the lanyard around your neck; this can be an unsafe practice, particularly when doing any technical climbing, difficult scrambling, or when climbing over and under fallen logs, due to the possibility of strangulation. Furthermore, most lanyards are so short that the compass cannot be used effectively while it is around your neck anyway.
Of all the optional features, the declination adjustment is the most useful.
The primary advantage of the mirror is that most people can obtain more accurate compass readings with a mirrored compass.
A bearing is the direction from one place to another, measured in degrees of angle with respect to an accepted reference line. This reference is the line to true north, also called a meridian.
The compass is used for two basic tasks regarding bearings: 1.To take, or measure, bearings. To take a bearing means to measure the direction from one point to another, either on a map or in the field. 2.To plot, or follow, bearings. To plot, or follow, a bearing means to set a certain bearing on the compass and then to plot out, or to follow, where that bearing points, either on the map or in the field.
If the compass has no sighting mirror, hold it at or near arm’s length and at or near waist level, with your arm straight at about a 45° angle from your body
With a sighting mirror, no such compromise is necessary. Fold the mirror back to about a 45° angle and hold the compass at eye level, with the sight pointing at the object
The centerline of the mirror should cross the pivot point of the magnetic needle. In either case, hold the compass level. Keep it away from metal objects, which can easily deflect the magnetic needle, giving you a false reading.
difference between the direction to true north and the direction to magnetic north, measured in degrees, is called magnetic declination. Most compasses will need a simple adjustment or modification to correct for declination.
The amount of declination changes over time, by as much as one degree every five years in some places in the United States.
the line of zero declination (called the agonic line)
Along this line, the magnetic needle points in the same direction as the geographic north pole (true north), so no correction for declination is necessary.
The true bearing is a measurement of the angle between the line to true north and the line to the objective,
As in Washington state, travelers in all areas west of the zero declination line could add the declination to the magnetic bearing to get a true bearing.
If you have a compass with adjustable declination and set it for a declination of 16° E, as for western Washington state, then, once properly adjusted, the pointed end of the declination arrow will point to 16°, as
TIP: When using the magnetic needle in the field for taking and following bearings, always remember to align the north-seeking (red) end of the magnetic needle with the pointed end of the declination arrow to box the needle.
A better way of working with a back bearing is to keep the original bearing at the index line, and rotate the compass until the south-seeking end (the white or black end) of the magnetic needle is aligned with the pointed end of the declination arrow,
Ferrous objects such as iron and steel will deflect the magnetic needle and give false readings.
Whenever you measure or plot bearings on a map, it is a good idea to first guess at the answer, based on your knowledge of the cardinal directions. Then if the bearing you carefully measure or plot is nowhere near your original guess, you may have made one of those 180° errors.
It is a good idea to carry your compass in a place that is readily accessible, so that you can easily and quickly check your compass without taking off your pack. Carrying your compass in a cargo pocket will accomplish this. If it is inconvenient to get to your compass, it is unlikely that you will use it when you should.
When taking and following bearings in the field, always align the pointed end of the declination arrow with the north-seeking (red) end of the magnetic needle (box the needle). •Never use the magnetic needle or the declination arrow when measuring or plotting bearings on the map. Just make sure that the N on the compass dial is toward north on the map, not south, as a check to ensure that the compass meridian lines are not upside-down.
The goal of orientation is to determine that precise point on Earth’s surface where you now stand. You can represent your position by a mere dot on the map. This is known as point position. There are two lower levels of orientation. One is called line position: you know you are along a certain line on a map—such as a river, a trail, a ridge, a compass bearing, or a contour line—but you do not know where you are along that line. The lowest level of orientation is area position: you know the general area you are in, but that is all. The objective of orientation is to determine your exact point
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The closer an angle of intersection is to 90°, the more accurate the point position will be.
The technique of taking and plotting bearings from landmarks is more accurate if you can see three landmarks and plot three bearings. The result will be a small triangle (called a “cocked hat,” see figure 26). Your position is most likely within this triangle.
