This is slightly different from grid north, and the difference between them varies in different areas of the world and over time. Over short distances it should make little difference to your navigation but if you are walking on a single bearing for a very long distance in open countryside you need to compensate for it in order to navigate accurately.
An excellent use of a compass is to help you set the map, aligning it so that it corresponds to the surrounding landscape. This makes it much easier to relate the map to what you see on the ground. Many compasses have a clinometer built in the compass house. This is used for measuring inclination of slopes. To measure the map, you need a scale of some kind. Many of our compasses have scale lanyard with two scales on it; , and , which helps you measure the distance of your hike.
Many Silva compasses come with a magnifying lens built into the baseplate. This is useful for reading the map and for precision map work. The Earth and its magnetic zones work in mysterious ways, and to navigate accurately you need to make sure you have a compass for the place where you are at the moment. Different compasses work for different parts of the world. Hence be aware if you plan for an adventure on the other side of the world! However, at Silva we also have global compasses that works in any magnetic zone.
The degree and the direction of declination is shown on the map. On many of our compasses, you can compensate for magnetic declination by using the fixed declination correction scale inside the capsule.
Some of our compasses are equipped with an adjustment screw for compensating the declination more permanently. From there moving clockwise the right side is east, the bottom south, and the left is west. The parallel vertical lines on the map are there for you to line up your compass to orient everything in the right direction. Since a map is only two-dimensional, contour lines are used to show changes in elevation. The space between two lines represents a grade.
The closer the lines are together the steep the slope. Depending on the scale of the map, the difference in altitude between the lines can be anywhere between 10 and 50 feet. The legend of the map will list this height. Major increments and mountain peaks will show the elevation on the map.
Just like a model car, maps use a scale to let you know how much the actual terrain has been shrunk down. Common scales are , and , This means one inch on the map is 25, inches on the ground. While compass needles point in a northerly direction, they are not targeting True North most of the time. The North Pole is the point at which maps are oriented to while compasses aim at magnetic north which is a slowly moving spot in the Canadian arctic.
The difference between True North and Magnetic North is declination. The difference in degrees between the two of these points varies depending on where you are. In North America, the two coasts are off by around 20 degrees. As you move into the center the amount decreases. This is important to compensate for, especially when traveling over open land because over a distance you can up miles away from where you think you are.
If you are in the west you will adjust to the east and vice versa to compensate for the difference. East adjustments are positive and west are negative. So you would subtract that number from each of your calculations to find true north.
Most maps will have the declination listed in the legend but check the date on the map as the angle changes slightly each year. Some compasses have a declination adjustment which allows you to adjust the orienting arrow so when the bezel is set to the north with the needle in the dog house you are facing true north.
Magnifier for detailed map reading. The direction of travel arrow shows the direction that you want to travel along or the bearing you are taking. It is fixed parallel to the sides of the base plate and aligned with the fixed index line on the edge of the compass housing number 6.
Compass scale displayed along the edge of the base plate so you can measure distances on maps.
0コメント