Question about compass & orienteering

[DrRichardCranium]

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]

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]

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]

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]

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]

Or we could ask God to put the magnetic north back up where it belongs. He's slacking.

[MuddyWaters]

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]

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

[SkeeterPee]

why not set your declination on your compass if you have one that is adjustable?

[Shutterbug]

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]

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]

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]

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.

[rhjanes]

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]

Here's a post I made in a series of them on navigation.

http://artofwayfinding.blogspot.com/...ling-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]

Here's a post I made in a series of them on navigation.

http://artofwayfinding.blogspot.com/...ling-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]

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]

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?

[JohnHuth]

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]

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?