Declination is caused by the magnetic pole not being at the true North geographic pole so depending on where you are on Earth you may need to compensate for the difference.
However, if you're using quality USGS topo maps, they show declination on them. That too may vary, depending on how old the map is, as the magnetic pole moves around. If you want to you can check with a local surveying company and get up to the minute declination info. I myself don't bother with it. I just orient the map using compass and the mag. North arrow instead of the true North arrow and go from there.
Once you orient the map, there are two things you can do with map and compass: 1) find out how to get where you want to go and 2) find out where you are if you don't know.
For 1), put a corner of the compass on the place on the oriented map where you are so the edge of the compass is along your route of travel to where you want to go. Turn the bezel of the compass so the needle and North arrow line up, then read the compass direction you need to travel where the direction of travel arrow intersects the azimuth ring of the compass, where the degrees are indicated. Sight along the compass, standing with it in your hands, to identify a clearly identifiable landmark in the direction you wish to go, and walk to that landmark, repeat as needed until destination is reached.
For 2), identify three CLEARLIY identifiable landmarks around you, each in a different direction. Sight along your compass, using the direction of travel arrow and with the needle lined up with the North arrow, to each landmark and note the bearing, degrees to each landmark. On the map find the land marks, a distinctive hill, or a cove in a lake, a house, etc. and draw lines in the directions you've gotten from each landmark. They should intersect in ideally a point, but most usually in a tiny triangle, you are in the triangle or at the point where the lines intersect.
Get the BSA Orienteering merit badge book, and Bjorn Kjellstrom's book, "Be Expert With Map and Compass" and practice around the yard or at a park. One good exercise is to put a small flat object, like a tin can lid, on the ground as a starting point, then sight a random azimuth to a distant landmark. Follow that for a certain number of paces (a pace is two steps), then add 120* to the first bearing, sight on a landmark and follow that the same number of paces. Then add 120* to the second bearing, get a landmark and follow that the same number of paces. If you're accurate in sighting the bearings and counting paces, you should end up exactly where you started, most often you'll be very close. 120* X 3 = 360*. Use a flat object as the starting point to keep yourself honest so you can't easily see it and just walk back to it.
Hope that helps.
Reply With Quote
Originally Posted by rottenpossum
Bookmarks