I can assure you that you’re factoring it in this way, too, but I also understand what you mean. Remember that excellent topo maps can also have their declination line in the bottom corner, making it easier to orient a line of travel against true north lines & doing the simple math step if necessary. Orienteering maps of course have meridian lines drawn for magnetic north, but they may not be the best idea for long distance navigation.Originally Posted by Greg Miller
So many stories to tell about being prepared, I don't know where to start. So I'll pick one I don't think I've told on this forum before.
One time I went off-trail to investigate a bubbling sound because... you know... that's where the shots are. I slipped just a bit. My shoe was impaled by a piece of rebar sticking up next to the culvert. Ripped a piece of skin between toes, nothing serious at all.
I was glad I had two gallons of water in my pack to cleanse the wound.
Why would anyone carry two gallons of water? It was just dead weight... this was a training hike. I was getting used to a 35-pound pack. But it also meant I could pour it all out and have practically no weight for the hike out.
I did not suggest that it wasn't factored in. Just that there is no need for the navigator to consciously factor it in. (other than to use the magnetic north line instead of true north line). In fact the navigator doesn't need to know the declination value at all. Nor take extra steps to account for it.
The earth, and its magnetic field, is a very dynamic and ever changing place. In fact, many people believe that the earth is currently entering a period of magnetic reversal (north becomes south on the compass) which has occurred many times in the past. But for the sake of argument suppose you could navagate between distant points A to B without the use of a compass and arrive with just a 2 degree margin of error - which would be quite a feat if the distance between A and B is appreciable. My last long distance hike was 165 miles long. A 2 degree error translates to being just shy of 6 miles off target and your map wouldn't help you much being that far off the mark. What would you do then?
The best policy is to constantly reorient yourself as you go and the best way to do that is to factor in the MD. Sometimes the terrain appears isotrophic - especially in the winter - and you can't always navigate by the way things look around you. Have you ever encountered two different landforms that appear identical from a distance? Imagine yourself as a soldier calling in artillery or air support or an injured hiker calling for rescue. You want to be able to state exactly where you are and not have them going several miles away.
Thomas
We agree that re-orienting when reaching obvious landmarks is a good policy. I think traveling 165 miles without doing so would be exceedingly rare for the vast majority of us. So being 6 miles off target is just a straw man. Perhaps you can see far enough in your area where 2 degrees can be a factor, but where I travel, you can't typically see far enough where it would matter. And when you can see far enough, you can generally see obvious landmarks to correct your bearing, assuming you are good enough to sight with less than 2 degrees of error. And, again. all of this only matters if you are not using other navigation tools such as following ridges, valleys, streams to confirm your line of travel. And perhaps it is just me, but I have never accounted for any drift in declination over time, and it has never affected my arrival at my destination in any way. YMMV.
A dog that knows the way home... I am only half kidding.
Several years ago I went into the woods not far from where I grew up. I was scouting for some possible shots for the next day. I knew the trails, shortcuts and features (some particular tree, a particular rock, etc.). It was drizzling and looked like it was going to clear up at any minute - the sun was out here and there. About two hours later, a heavy fog rolled in - I couldn't see two feet in front of me, couldn't recognize the land features but soon ralized that I was going in circles. In some places the trail was not well-worn and wasn't sure if I was still on it. Late afternoon turned into early evening... My cosin's dog always came along on my treks and at one point I said to the dog (in Italian)Let's go home".I just followed her and about an hour later the fog was fading behind me. I also realized that I had been no more than 1km away from home. Since then, i always carry a compass...
Last edited by Renato Tonelli; 30-Apr-2012 at 19:51. Reason: Sp
I was going to respond but Renato brought up a common situation:Perhaps you can see far enough in your area where 2 degrees can be a factor, but where I travel, you can't typically see far enough where it would matter.
If you know the azmuith of whence you came you can, with a compass, retrace it. A serious pathfinder will notate on the map or in a notebook the distances traveled and azmuiths taken. Only then could you retrace your path in such circumstances with a degree of confidence. Travel under heavy canopy is best acomplished by azmuiths. But that requires you to keep track of the distances traveled both along the line of azmuith and off of it when making detours. You must return to the correct azmuith after each detour. If the distance between point A and point B is large, you're going to be a little off mark but not as you would without striking out on a path by azmuith.A dog that knows the way home... I am only half kidding.
Several years ago I went into the woods not far from where I grew up. I was scouting for some possible shots for the next day. I knew the trails, shortcuts and features (some particular tree, a particular rock, etc.). It was drizzling and looked like it was going to clear up at any minute - the sun was out here and there. About two hours later, a heavy fog rolled in - I couldn't see two feet in front of me, couldn't recognize the land features but soon ralized that I was going in circles. In some places the trail was not well-worn and wasn't sure if I was still on it. Late afternoon turned into early evening... My cosin's dog always came along on my treks and at one point I said to the dog (in Italian
Thomas
Thomas
Do me a favor, and calculate how many hundredths of an inch that 2 degrees represents for one mile on a map where one mile is represented by 1.5 inches. The let's talk about how likely the map maker is to have that level of accuracy, how likely the map is printed to that level of accuracy, how likely it is that, in the wilderness, you can orient your map that accurately, and how likely, in the wilderness, you can walk one mile with that level of accuracy, and how likely the cumulative error in the whole system makes any sense at all to talk about that level of accuracy.
OK a declination story.
My buddy Tom (Mr. Search and Rescue) and I were the only ones of the group who wanted to bag a peak on our first trip of many in the Sierra. We were camped at one of the Mills Creek Lakes and headed on a day hike to Mount Abbott for a nice walk-up. We got to the saddle and I aimed my compass at the appropriate bearing and started towards the mountain.
It seemed like a really long approach, but with the top in sight, Tom decided to take a break. I did a bit more scrambling. It was a bit dicey but nothing worse than climbing the fireplace next to my house to get on the roof. So I get up and find the register.
I yelled down... Hey Tom, this is Bear Creek Spire.... I'm NOT climbing down a Class 4 mountain without ropes.
Cartographer's licence. Something I discovered many years ago.
Steve.
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