Map and compass tutorial

[iAmKrzys]

I find understanding declination quite useful but my most frequent use case is far from typical - when I navigate to a waypoint off trail using my GPS (translation: "when I bushwhack to a geocache") I look up the bearing (relative to true North) on my GPS and then use my "real" magnetic compass instead of the electronic compass in my GPS. The reason is that I got tired of having to recalibrate my GPS compass while at the same time my real compass is a lot more stable. All I have to do is to correct for declination.

 

[jniehof]

I look up the bearing (relative to true North) on my GPS and then use my "real" magnetic compass instead of the electronic compass in my GPS.

Most GPSrs can be set to give magnetic bearings, if you'd prefer.

 

[iAmKrzys]

Most GPSrs can be set to give magnetic bearings, if you'd prefer.

Thanks for the pointer. I searched the manual for bearing and came up empty-handed but then I searched the Web and found that this is buried under "North Reference" menu item. Interestingly this is mentioned in the manual in 9 words: "North Reference - sets the north reference of the compass." That's it! One thing that I must say about Garmin documentation is that it totally sucks. Basically you have to know that you can do something and then maybe you have a chance of figuring out how to do this, but forget about learning in depth about Garmin GPS functionality from its manual. That's really too bad because I think these GPSes are really good products.

 

[DayTrip]

Thanks for the pointer. I searched the manual for bearing and came up empty-handed but then I searched the Web and found that this is buried under "North Reference" menu item. Interestingly this is mentioned in the manual in 9 words: "North Reference - sets the north reference of the compass." That's it! One thing that I must say about Garmin documentation is that it totally sucks. Basically you have to know that you can do something and then maybe you have a chance of figuring out how to do this, but forget about learning in depth about Garmin GPS functionality from its manual. That's really too bad because I think these GPSes are really good products.

I agree. I think Garmin manuals are terrible. The model I have is fairly intuitive to use and I figured out most stuff just messing around with it for a few minutes but there are definitely things you need to realize are possible before you can even attempt to locate in the menus. I've Googled a few things to figure out how they are done after reading the "guidance" in the manual.

 

[HH1]

Hikerbrian,

Here's your statement of your ultimate training objective:

The scenarios I'm looking to prevent are: 1) Walking down the wrong trail in the wrong direction for an extended period of time; and 2) Getting slightly off trail and having no idea whatsoever how to get back to safety

If those are your two ultimate objectives, do you even need to worry about magnetic declination?

Say a person is in a region of 15 degree magnetic declination but is clueless about it. My view is that in most real world situations that 15 degree error would be accommodated while preventing your particular scenarios. Why not test a bunch of what-ifs to see what the outcomes are?

Whereas if someone in the same declination zone screws up a mnemonic or other memory device, then they're out 30 degrees and that for sure could be trouble.

I know what I suggest is not the proper way to instruct M&C, but given your constraints are there other options here?

Again, you have taken on a challenge that would cause a lot of us to take cover!

 

[Nessmuk]

Does 15 degrees make a difference? I show this Youtube video in my class when I get to making the point about what a croos-track difference a 15 degree error can make.

https://www.youtube.com/watch?v=EBwNwoDVT8E

Produced by Silva

 

[iAmKrzys]

Does 15 degrees make a difference?

A number of years ago I did this geocaching "field puzzle" with my kids where we needed to read some numbers off a historic plaque in town and use these numbers to determine distance and bearing to a physical container holding the log. We had to cover more than 2000 ft and then it struck me that the cache owner did not say whether he meant true or magnetic bearing and the difference between the two was about 500 ft !!! If the final destination were in the woods we could be searching for a proverbial needle in a haystack! Luckily only one of the choices lead to a park where we found the container but this really made me think how far off I could end up when going just a little bit off course.

 

[Nessmuk]

iAmKrzys,

The rough rule of thumb for calculating cross-track error is one part in 60 per degree of error (true only for relatively small angles). For example (to keep the math easy), if you travel in a straight line for 600 feet on a wrong azimuth, your cross-track error is 600/60=10 feet per degree of error. 15 degrees of neglecting declination will put you 15x10=150 feet in cross track error.

With your example, At 2000 ft, 2000/60=33.333, then 33.333x15=500 ft!!

 

[hikerbrian]

If those are your two ultimate objectives, do you even need to worry about magnetic declination?

Great question! And thanks others for 'doing the math' for me. I've thought through that question quite a bit. If a person knows they 'just need to go west' because they're off trail and they need to get to the highway, does it matter if they're 15 degrees off from true west? It's a fair and reasonable question. And I think the answer in that scenario is probably No, it doesn't matter too much. Same with the other scenario I outlined.

BUT. Then I asked myself how hard it really is to teach the critical concepts needed to account for declination, and what the reward for that extra work is. As I see it, it IS possible to teach new students how to account for declination without completely confusing everyone. Thanks to everyone who has contributed to this thread, I now have several ideas for how I might present that part in a clearer and more durable manner.

A secondary goal of mine is to give folks the critical foundation so they can dive in to M&C navigation without having to explicitly learn (or unlearn) anything I've taught them. So I think there's real value in teaching declination from the outset, even if there isn't bandwidth to get into much detail. Then when they pick up other tutorials or want to triangulate or whatever, at least they already know all of the critical language and concepts.

Finally, there are times when the 15 degrees really matters. Hitting Lion Head without dropping accidentally into Tucks or Raymand Cataract, for example. You want to get it right in that situation. You REALLY want to get it right. I don't want to set anyone up for an epic, life-endangering failure like that. I think I'd rather folks just 'didn't get it' than think they got it and then endanger themselves.