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DrRichardCranium
05-30-2016, 17:05
I live in Maryland where Magnetic North is about 10 degrees west of True North. Books on orienteering talk about converting True North on the map to magnetic north in the field, and vice versa, but my question is: why bother? Why not just forget about True North and when you orient your map, you orient it to Magnetic North and calculate your vector from that?( All my maps have two vectors printed on them, Magnetic North and True North)

So I orient my map to magnetic north, find out that my destination is at 240 degrees from magnetic north, and just use that figure in the field. What is the point of converting back and forth, instead of just doing everything in relation to Magnetic North?

firesign
05-30-2016, 17:21
I live in Maryland where Magnetic North is about 10 degrees west of True North. Books on orienteering talk about converting True North on the map to magnetic north in the field, and vice versa, but my question is: why bother? Why not just forget about True North and when you orient your map, you orient it to Magnetic North and calculate your vector from that?( All my maps have two vectors printed on them, Magnetic North and True North)

So I orient my map to magnetic north, find out that my destination is at 240 degrees from magnetic north, and just use that figure in the field. What is the point of converting back and forth, instead of just doing everything in relation to Magnetic North?

This explains it better than I can:

https://www.maptools.com/north_reference

Best of Luck

rocketsocks
05-30-2016, 17:27
Not all maps have both vectors. One thing I've done in the past is add my own to a map, takes about 3 min to do.

DrRichardCranium
05-30-2016, 17:30
Exactly what I was thinking. If your map doesn't have it (most of mine do) you could just find out the declination in your area and draw the vector in, using your compass as a protractor.

rocketsocks
05-30-2016, 17:41
Exactly what I was thinking. If your map doesn't have it (most of mine do) you could just find out the declination in your area and draw the vector in, using your compass as a protractor.
Should last for a couple hundred years till the next pole shift.

DrRichardCranium
05-30-2016, 17:44
Or we could ask God to put the magnetic north back up where it belongs. He's slacking.

MuddyWaters
05-30-2016, 18:21
all depends on what you are doing
most of the time your bearings are relative, and it doesnt matter. You rarely need to convert anything.


You orient the map so it matches the surroundings. , so you can look and see stuff in its correct position. You dont need to orient map to figure out bearings to follow relative to magnetic north, true north, or some other landmark. Its all on the map....as long as you know your position.

Even if you want to shoot your position relative to a landmarks, you still dont need to orient the map. Just shoot the bearing relative to magnetic north, and draw in on map relative to magnetic north. But that can require drawiing in magnetic north lines on the map to alighn your compass. So its easier to draw relative to true north, because those lines are already drawn in to align compass with. So you convert. not a big deal

Pedaling Fool
05-30-2016, 18:31
all depends on what you are doing
most of the time your bearings are relative, and it doesnt matter. You rarely need to convert anything.


You orient the map so it matches the surroundings. , so you can look and see stuff in its correct position. You dont need to orient map to figure out bearings to follow relative to magnetic north, true north, or some other landmark. Its all on the map....as long as you know your position.

Even if you want to shoot your position relative to a landmarks, you still dont need to orient the map. Just shoot the bearing relative to magnetic north, and draw in on map relative to magnetic north. But that can require drawiing in magnetic north lines on the map to alighn your compass. So its easier to draw relative to true north, because those lines are already drawn in to align compass with. So you convert. not a big deal
Yeah, if you're hiking the AT and all of a sudden decide to walk to the beach, you don't really need to worry about magnetic declination, but if you want to land at a specific beach, than you had better mind your declination:D

SkeeterPee
05-30-2016, 19:52
why not set your declination on your compass if you have one that is adjustable?

Shutterbug
05-30-2016, 20:13
I live in Maryland where Magnetic North is about 10 degrees west of True North. Books on orienteering talk about converting True North on the map to magnetic north in the field, and vice versa, but my question is: why bother? Why not just forget about True North and when you orient your map, you orient it to Magnetic North and calculate your vector from that?( All my maps have two vectors printed on them, Magnetic North and True North)

So I orient my map to magnetic north, find out that my destination is at 240 degrees from magnetic north, and just use that figure in the field. What is the point of converting back and forth, instead of just doing everything in relation to Magnetic North?

If you are pilot, it makes a difference. If you are hiking it doesn't.

Hikingjim
05-30-2016, 22:43
usually I just like to adjust the declination on my compass so that I can just look at the map as is and not care about declination for the rest of the trip.

But if it shows both on a map, then you're right, you can navigate by using magnetic north if you want... and ignore any conversion

Wise Old Owl
05-30-2016, 22:55
Well Dr Cranium, to best answer your question prior to GPS is makes a world of difference - your location is 10 in Massachusetts, its 15 and overtime it has changed here in PA it was 12 now its 13 in my lifetime. Good American compass have adjustments for this..most don't. IF you are backwoods with map and compass its just common sense - otherwise its following white blazes and all you have to do is make it back to the trail after a bathroom break.


hope that helps... it is a good question.

cmoulder
05-31-2016, 12:02
For the most part it doesn't matter if you consistently use magnetic north as your reference for everything. For instance, if you're using a phone app or stand-alone GPS, then those must also be set to "magnetic north" to avoid any confusion. Also, most maps are printed with their edges aligned to true north, so you end up aligning them a little 'cock-eyed' until you get used to the whole process.

Personally, I like to correct declination for true north because declination changes greatly depending upon where you are and true north is always the same. About 13 deg West where I live, about 20 deg East in the Northwest.

And, as someone noted above, declination changes over time because the magnetic pole drifts and therefore it can be off a few degrees on old maps, so it's also best to find out the current declination in the area you're visiting. Plenty of web-based sources, such as THIS (http://www.magnetic-declination.com/#).

rhjanes
05-31-2016, 12:08
Get a compass that you can adjust it at......but also, check the maps! I do a lot of orienteering and all the newer maps (last 10 years) are ALREADY declinated......just show up and the map they hand you is already set.......

JohnHuth
05-31-2016, 12:30
Here's a post I made in a series of them on navigation.

http://artofwayfinding.blogspot.com/2014/08/magnetic-and-true-north-dealing-with.html

The answer is that you have multiple ways of taking declination (or variation) into account - can draw lines of variation on the map, to make it easy, can offset the compass needle, can learn the add/subtract rule, can get a compass that allows a change in declination. All work - best to find one that works for you. Personally I don't like the add/subtract rule, but the military loves it. But, as the saying goes, "there's the good way, the bad way, and the Army way"

rocketsocks
05-31-2016, 13:09
Here's a post I made in a series of them on navigation.

http://artofwayfinding.blogspot.com/2014/08/magnetic-and-true-north-dealing-with.html

The answer is that you have multiple ways of taking declination (or variation) into account - can draw lines of variation on the map, to make it easy, can offset the compass needle, can learn the add/subtract rule, can get a compass that allows a change in declination. All work - best to find one that works for you. Personally I don't like the add/subtract rule, but the military loves it. But, as the saying goes, "there's the good way, the bad way, and the Army way"thanks for the textbook blog, enjoying that thus far, id be curious if ya have anything regarding using a sextant? you could post.

AfterParty
05-31-2016, 15:13
If i am doing intersection resection I'd probably do the conversations. Cause at that point I'm lost and want to be sure.

cmoulder
05-31-2016, 15:45
If i am doing intersection resection I'd probably do the conversations. Cause at that point I'm lost and want to be sure.

LOL, I have no idea what the hell this means. Can anyone translate? :confused:

JohnHuth
05-31-2016, 16:01
id be curious if ya have anything regarding using a sextant? you could post.

I could post something on the standard way of doing celestial with a sextant, sure. Do you own one? If so, what kind?

Greenlight
05-31-2016, 16:08
It is easier to simply add the declination to your compass and drive on.


I live in Maryland where Magnetic North is about 10 degrees west of True North. Books on orienteering talk about converting True North on the map to magnetic north in the field, and vice versa, but my question is: why bother? Why not just forget about True North and when you orient your map, you orient it to Magnetic North and calculate your vector from that?( All my maps have two vectors printed on them, Magnetic North and True North)

So I orient my map to magnetic north, find out that my destination is at 240 degrees from magnetic north, and just use that figure in the field. What is the point of converting back and forth, instead of just doing everything in relation to Magnetic North?

rocketsocks
05-31-2016, 16:30
I could post something on the standard way of doing celestial with a sextant, sure. Do you own one? If so, what kind?
No I sure don't, just always found it neat. I know there's stuff on the net, I guess I was asking if you had blogged about it in your own style as your compass article read very easy for me. Thanks for the consideration.

JohnHuth
05-31-2016, 17:05
I guess I was asking if you had blogged about it

Not yet, but I've been getting similar requests, so I think I'll start to put something together. I'll use a plastic Davis Mk3 sextant as the teaching instrument, as they're affordable, available, and a good beginner's sextant (easy to use and surprisingly accurate).

southernfire97
05-31-2016, 17:16
I am a regular on ESEE knife forum. You can go to their site jungletraining.com, go to links and pull up the navigation course. It's a complete PowerPoint on how you navigate with a compass. Extremely good information and it's free.

southernfire97
05-31-2016, 17:18
https://randallsadventure.com/wp-content/uploads/2015/11/map-compass.pdf
Here's the link

AfterParty
05-31-2016, 17:54
LOL, I have no idea what the hell this means. Can anyone translate? :confused:
Finding 2 known points and figuring out where you are, or someplace is.

rocketsocks
05-31-2016, 20:03
Not yet, but I've been getting similar requests, so I think I'll start to put something together. I'll use a plastic Davis Mk3 sextant as the teaching instrument, as they're affordable, available, and a good beginner's sextant (easy to use and surprisingly accurate).fantastic, thanks look forward to checking it out sometime.

DrRichardCranium
05-31-2016, 23:28
That's some really great stuff right there.

John B
06-01-2016, 08:49
It seems that almost every month, each REI store offers a compass/map reading course. It's a 2-hour course, $50 for non-members, $35 for members. I'll be taking the June 13 course at the Cincinnati REI.

Another Kevin
06-01-2016, 15:48
Maps virtually always have true gridlines ruled on them.

I could scribe my maps with magnetic gridlines, and sometimes do...
... but it's less work to simply set the declination of my compass and then not worry about it.

(I also know how to do Timid Virgins Make Dull Company At Weddings - which you need to do in a vehicle, but deviation is negligible with a handheld compass away from vehicles, buildings, railroads and power lines.)

cmoulder
06-01-2016, 16:22
less work to simply set the declination of my compass and then not worry about it.

+1

KISS in action.

rocketsocks
06-01-2016, 16:25
Maps virtually always have true gridlines ruled on them.

I could scribe my maps with magnetic gridlines, and sometimes do...
... but it's less work to simply set the declination of my compass and then not worry about it.

(I also know how to do Timid Virgins Make Dull Company At Weddings - which you need to do in a vehicle, but deviation is negligible with a handheld compass away from vehicles, buildings, railroads and power lines.)well I never heard that acronym, what it's all about?

cmoulder
06-01-2016, 17:02
http://wawewi.com/mnemonics/index.php?p=83

true+variation=magnetic+deviation=compass+add west (if east of the magnetic declination "zero line"

http://www.navigationtips.com/wordpress/wp-content/uploads/2014/08/East-and-West-Declination-for-the-U.S.1.jpg

Sarcasm the elf
06-01-2016, 17:39
Maps virtually always have true gridlines ruled on them.

I could scribe my maps with magnetic gridlines, and sometimes do...
... but it's less work to simply set the declination of my compass and then not worry about it.

(I also know how to do Timid Virgins Make Dull Company Add Whiskey - which you need to do in a vehicle, but deviation is negligible with a handheld compass away from vehicles, buildings, railroads and power lines.)

Kev: That nemonic was updated ages ago...

rocketsocks
06-01-2016, 18:10
http://wawewi.com/mnemonics/index.php?p=83

true+variation=magnetic+deviation=compass+add west (if east of the magnetic declination "zero line"

http://www.navigationtips.com/wordpress/wp-content/uploads/2014/08/East-and-West-Declination-for-the-U.S.1.jpgthankee :)

cmoulder
06-01-2016, 18:29
Kev: That nemonic was updated ages ago...

LOL, I like "Add Whiskey"

Reminds one of the Ogden Nash ditty: Candy is Dandy but Liquor is Quicker :)

rickb
06-02-2016, 06:24
Its interesting to ponder why orienteering compasses (meaning those used designed for the sport of orienteering) like thumb compasses don't adjust for declination.

I think they see benefit in using Magnetic North marked on their maps and lining up with that and keeping things simple.

I think it is good to know that on the east coast the compass needle points a bit left of true north, and on the west coast it points a bit right of true north and such, but for most practical purposes one can be very well served alomg the AT with a compass-- even if you ignore declination all together.

rocketsocks
06-02-2016, 10:24
Its interesting to ponder why orienteering compasses (meaning those used designed for the sport of orienteering) like thumb compasses don't adjust for declination.

I think they see benefit in using Magnetic North marked on their maps and lining up with that and keeping things simple.

I think it is good to know that on the east coast the compass needle points a bit left of true north, and on the west coast it points a bit right of true north and such, but for most practical purposes one can be very well served alomg the AT with a compass-- even if you ignore declination all together.
Yup you're right, it'll work, but could start a domino effect of the already epidemic dumbing down of our yute.

Another Kevin
06-02-2016, 15:53
Kev: That nemonic was updated ages ago...

There's also the one that runs the other way: Chicago Dead Men Vote Twice At Elections

Compass + Deviation = Magnetic + Variation = True (Add East)

Hikingjim
06-02-2016, 16:03
http://wawewi.com/mnemonics/index.php?p=83

true+variation=magnetic+deviation=compass+add west (if east of the magnetic declination "zero line"

http://www.navigationtips.com/wordpress/wp-content/uploads/2014/08/East-and-West-Declination-for-the-U.S.1.jpg


I stick to hiking straight up that red line so that I don't even have to worry about it!

Another Kevin
06-02-2016, 16:53
I think it is good to know that on the east coast the compass needle points a bit left of true north, and on the west coast it points a bit right of true north and such, but for most practical purposes one can be very well served alomg the AT with a compass-- even if you ignore declination all together.

True enough. But I own a mirror-sight baseplate compass, so that's what I bring. (Having a small mirror comes in handy for other purposes, anyway.)

Orienteering is much less about compass navigation as it is about terrain reading. A thumb compass gives you enough information to orient the map roughly, and then you're typically running a handrail or running for a capture feature. You're very rarely dealing with having to take an accurate sight.

I do a fair amount of off-trail travel, where an accurate sight, accounting for compass variation does matter, at least sometimes. It certainly matters if you're determining position with resection or estimating a distance with intersection, or you want to minimize the amount you need to "aim off" from an approach point on a distant handrail.

Elf took this picture at one point when I was showing him some of the techniques.

https://c2.staticflickr.com/4/3877/14738413825_f10056c98b_z.jpg (https://flic.kr/p/osodXc)

We recovered position - together with an error estimate, by sighting on the abutment of the bridge at far right, the barn near the highway at left center (the pattern of the buildings was visible on a topo), and the peak at left, resecting all those lines back to the ridge we were standing on. We were as near the ridge top as made no difference, so could use the ridge itself as a fourth line of position.

The resections clustered pretty closely. When I had him cross-check with GPS, it was pretty much spot on.

Of course, I knew where the nice overlook was, but it's good to run through the exercise.

By the way, since Nature has no scale, I'll mention that the near shore of the lake there is about five miles off, the peak beyond is 7.4 miles from where we're standing, and the bridge is 8.1 miles. There's about three thousand feet of elevation difference between us and the valley floor, with over half of it in the first half mile. In other words, that cliff is a technical climb. We hadn't climbed it. We'd bushwhacked up the ridge from the other side and had been about a day and a half playing around in a huge trail-less space back there by the time we reached this spot.

rickb
06-02-2016, 19:01
Sound fantastic, Another Kevin.

I really think its time that you updated the tag line under your name. Seriously.

Another Kevin
06-02-2016, 19:32
Sound fantastic, Another Kevin.

I really think its time that you updated the tag line under your name. Seriously.

I remain clueless about thru-hiking, never having attempted it, and keep the label to thumb my nose at those who worship the thru-hike and think that being a weekender means that I'm clueless.

cmoulder
06-03-2016, 06:57
This is a great exercise, better than any classroom.

I did something similar for my nephew, with him actually manning the compass and map, using only a couple of bearings from some very clear landmarks. And then he matched it up with the topo contours, bringing the landform aspects into the equation. Accomplished in a few minutes a lesson that will be remembered a long time.

Now reading Harold Gatty's Finding Your Way Without Map or Compass (http://www.amazon.com/Finding-Your-Way-Without-Compass/dp/048640613X?ie=UTF8&*Version*=1&*entries*=0). Old School and really enjoyable (well, to me anyway).

JohnHuth
06-06-2016, 08:44
Its interesting to ponder why orienteering compasses (meaning those used designed for the sport of orienteering) like thumb compasses don't adjust for declination.

I think they see benefit in using Magnetic North marked on their maps and lining up with

Yes, exactly. I also mark up my maps this way. I make the distance between the lines 1 mile (or nautical mile on nautical charts) to make it easier to estimate distances - use the compass lanyard - curl it around on your path, and then pull straight to compare to the lines.

lemon b
06-12-2016, 04:35
I learned how to read and follow a map at age 10. I adjust. Its 13 degrees here. Pace count is important, knowing how elevation effects your pace. Fact is the AT is so well marked these days a map is more of a safety tool now adays. Also in thick wood the elevation lines are more important than shooting a reference point because that point is sometimes difficult to find.

DrRichardCranium
06-12-2016, 14:30
I just found out that Samsung smartphones contain a pressure sensor. So you can download an altimeter app. Use your elevation to find where you are on a topographical map.

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