Dealing with Declination

[RoySwkr]

Drawing lines on a map? Never did it. In fact I've never even seen anyone's map with lines drawn on it when I've gone whacking.
... I just look at the map on Topozone before I go and remember 13 or 14 or 15 degrees. I'm up to that task.

I have seen maps that people have drawn lines on. I have also seen maps in which the grid lines are oriented to magnetic north, usually orienteering maps but if I recall correctly some AMC maps used to do it.

Like you, I make the adjustment mentally if I just look at the map. If I'm setting a compass bearing I set it from the map grid then twist an extra 15 degrees or whatever. No big deal.

Seems odd to me that a compass would be designed in a way in which one cannot read the declination setting.

I probably have over a dozen compasses and none of the hiking ones have a declination setting.

I have a vehicle-mount compass that I never used that allows you to adjust the declination to include the magnetic field of the car but I don't think you can read how much you set it by. Of course if you drive the car far enough the local declination may be different so you need to either recalibrate or adjust for the difference from where you set it.

 

[Toe Cozy]

Declination - pah! If you don't use a map and compass you don't need to worry about it! Who needs that kind of stress when you're out in the woods???

I just started off trail hiking with map and compass this past fall, so what H do I know. Not much. But, I practice the parallel line drawing method. I clear off the kitchen table, get out my quad map, tape it down with painter's tape get my pencil and start making lines. My husband comes in and says, "uh-oh, what are you scheming now? Got big plans for the weekend?" I really like having the magnetic north lines drawn in ahead of time. However, I've only ever done it that way. I would like to get some practice with other methods though. I have done simple adding of degrees to get our desired bearing when I learned some nautical navigation for a sailing class but I haven't done that for hiking yet.

I think there is a lot of value in spending time getting to know your map for a particular adventure before heading out. Drawing lines on it helps me with that.

That being said...remember, what the H does Toe Cozy know? Not much! And besides that, have you had problems getting lost and or being confused/frustrated with your previous method of working with declination? If not, maybe no change is needed for you.

 

[cbcbd]

I spend plenty of time looking maps over but I haven't done the drawing of the lines trick. I realize it helps but my compass has adjustable declination and I have gotten used to pre-adjusting for trips.

Either way will work but I am a strong proponent of getting a compass with at least adjustable declination - even if you understand the math and reason it saves a lot of time and grief, especially if your mind isn't at 100%, to just have that declination set - and who knows, maybe you didn't mark that one map, or you lost your map, are using someone else's map, or your friend Mike threw your map away while you guys were in the woods looking for some witch.

 

[cushetunk]

Y'all use your compass so much that 15 degrees matters? I just follow the terrain and use backstops.

I used to draw magnetic north lines on maps, then I got a declination-adjusted compass, then I lost it somewhere, then I realized I don't use a compass for much beyond 45-degree increments anyway. Even when bushwhacking.

To help me switch between TN and MN, I just remember that magnetic north is somewhere up above Wisconsin or something, and as a result TN is always further in the direction I am from Wisconsin. Got that? Conversely, you can remember that MN is always leaning more towards Wisconsin than TN. This rule especially shines if you're in Wisconsin, but maybe don't try this at home outside the north-west hemisphere area.

 

[Neil]

This rule especially shines if you're in Wisconsin, but maybe don't try this at home outside the north-west hemisphere area.

If I need to know what hemisphere I'm in I flush a toilet.

The thing I like about all the precision is ...all the precision. But I agree about backstops, especially if it's a stream or a lake. Anyway, who needs a compass or a map when you can follow the arrow on a gps?

Wait a sec, I think there has been a debate already on gps vs. compass. My bad.

 

[sardog1]

Nighttime bushwhacking does not succeed easily without a compass and appropriate declination adjustment. Above-treeline excursions in bad weather do not succeed easily without a compass and appropriate declination adjustment. Opinions to the contrary will be given an opportunity to test the proposition at a mutually agreeable time. Loser buys the beer -- if we make it out.

Competitive orienteers draw the lines so they can use their compasses and ignore the issue while they're racing through the woods. These folks have forgotten more about matching terrain and map than most of us will learn in our lifetimes. There's a reason they take declination into account nonetheless.

Personally, I'd like to see an image of a compass on which one cannot discern whether a declination adjustment has been made. Some are sold without one, some are sold with a half-@##$%! one, and some have the bezel adjustment that DougPaul and others and I favor. None in my vast personal experience fall in the category of "cannot be determined." Maybe we're not understanding the context?

Here's a chart that will aid the uninitiated re: declination (and perhaps others . . .) Isogonic Chart

(Vinny rocks. I was thinking this very afternoon of using his brilliant track analysis to show the value of tracking to fourth graders. But they're a little young for the whole Vinny experience.)

 

[Stan]

Declination varies with location and over time, though ever so slightly. I never adjust my compass, I always do the calculation and adjust the bearing. Unfortunately, even after many years of making this adjustment I still have to stop and think, do I add or subtract? The only way I know for sure if my "west is best, east is least" aid is correct is that I try to visualize the true and magnetic poles and make the calculation from there.

Compass adjustments can be confusing and, when wrong, can be inconveneient to say the least. I suggest people become familiar with various approaches to map and compass and then stick with the approach that is most comofrtable and intuitive for them.

 

[Fitz]

Varies with Time

Exactly. Declination varies with time and location and on average changes 4 minutes per year in Boston for example. So if you are relying on old topos, you may be significantly off. Here is a declination calculator for your use:

http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp

I keep waiting for a reversal any time now myself. The field is acting funky lately, planet earth is overdue, but a big switch apparently maybe off a millenium or so.

 

[Peakbagr]

"even if you understand the math and reason it saves a lot of time and grief, especially if your mind isn't at 100%, to just have that declination set"

Why I write the bearing on tape on the reverse of the compass when I think it'll be necessary.

 

[marty]

Thanks everyone for the insightful and passionate replies I guess the big takeaway here is being able to correctly understand and apply the principles of determining declination. The best method is the one the works best for you.

Regards,
Marty