Nav Work 101 - Cardinal Directions and Declination

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Lurch
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Nav Work 101 - Cardinal Directions and Declination

Post by Lurch » January 25th, 2013, 7:21 pm

Alright guys, time to kick this beast off!

Other Nav Threads
Nav 102 - Crazy Magnets and Stuff
Nav Work 103 - Pacing, Obstacles, and Nav-Nerds

If you want to get into legitimate navigation, you need a general understanding of what's going on. My writeup's will be simple, practical navigation, not the elaborate primitive survival, star reading, elaborate/impractical type navigation that you read of in most books. So I'm going to start this from the uber basic and we can work our way forward. Please please please feel free to ask questions, I'd love to get legitimate discussions going from these threads, but if not, if I can pass out some common sense nav knowledge than I'll be happy either way. I usually do this in a powerpoint presentation and talk my way through most of it, so converting it to a thread will be new for me.

Cardinal Directions
The very basics for Nav would be the Cardinal Directions. We all should have learned this in elementary school, but I'll go over it again.
Image

Working our way around the circle, North is our "universal reference" that most people will go off of. If you imagine a circle, divided into 360°
North would fall at the top at 0° (aka 360°).
East would be on the right, at 90° (general sunrise)
South at 180°
West at 270° (general sunset)

Remember those numbers because they will be important when we get into map and compass work. The best way to avoid making mistakes is to develop some common sense self checks before you initiate any final step.

Note: There are NO negative bearings, and we do not do numbers above 360°. There is no 370°, and there is no -43°, everything should be between 0-360°, with 0 and 360 being the ONLY overlap.

Now that we've got our directions sorted out, we can talk about the different versions of them.. Since North is our reference, we'll focus on that right now, although technically there would be complete cardinal directions for everything.

North, North, or North?
The easiest way to break things down for people is that there are three different Norths

True North This is also considered 'Geographic North', or the 'North Pole', aka Santa's house. We lucked out in that our geographic poles are relatively stable (at least within a human lifespan) so we're not flying around space wobbling about. TRUE North is what we want to work in, at all times, because it is universal (well.. global I guess..), and doesn't matter where you are, or what you're looking at. We need to compensate for the others as we work with them to make everything referencing True

Magnetic North This is the Magnetic North Pole of the planet. We could get into what causes it and why it's where it is, but realistically that's not important. There are however a couple things that you need to understand.
  1. Magnetic North is NOT at the same location as Geographic North
  2. Magnetic North does move
Magnetic North is sliding at about 40 miles a year, which if you break it down actually works out to about 20 feet an hour. In geologic terms that's hauling! The biggest problem we have though is that the magnetic force lines unfortunately do not fall into our nice straight cardinal directions relative to their magnetic poles, and you must be careful about where you are on the planet to know how to compensate.

For US, in "north central oregon" you can fairly safely round to 16° East (we'll get into this later)

Grid North is the grid that the map projection is laid on. Because we're converting a sphere (roughly) to a flat piece of paper, there is a wee bit of distortion. That skews things to make them just a little bit off. For most uses though in our area Grid North will be less than 2° off, and will probably be in most people's margin of error, so it's relatively safe to use Grid and True as the same, until you start traveling outside of the gorge.

Declination
Declination is the difference in degrees, between True North, and Magnetic North. The needle on your compass points to Magnetic North (usually..) but since they are not in the same location as we pointed out earlier, and we want to reference everything off of True, we need to pull some shinnanigans to make everything work out correctly.

In our area, we are at roughly 16° East declination, meaning Magnetic is 16° East of True North.
declination.jpg
It's not *quite* that simple if you're traveling outside of the NW here, like we discussed earlier Magnetic lines don't travel straight

Image

This is one of the fundamental concepts that takes an insanely long time to fully comprehend. So I've found it's best to generally keep it simple, and not think about it too much. It is important that anyone using a compass understands declination however, and knows how to compensate for it.

If you are to take a bearing using your compass, which is not pre-declinated (something we'll get into in another thread) you are taking a bearing in magnetic. Since we want to reference everything in True, we should do the math to convert that bearing to true. We know Declination is 16°East, but do you add or subtract to convert to North? Luckily there is a handy little rhyme to help you remember.

Declination East, Magnetic Least

Simple as that! If you've got identical bearings in True and Magnetic, and you're in an area with East Declination the Magnetic should be the smaller bearing.

An example of this.. If you take a bearing to something in an area (like ours) with 16°E Declination and come out with 10°M (M for Magnetic), and you want to convert this to true, you would need to add 16° to that bearing.

10°M = 26°T

Declination East, Magnetic Least

These are the same bearings. So you may be asking, why bother converting to true? There's a big long explanation and there's the short one... But, BECAUSE YOU SHOULD! is the easiest. When you get into map work, everything is based on True, modern technology (GPS, Google Earth, Cellphones, etc) are automatically putting everything in True. True North is STABLE and doesn't move.. Everything, everywhere, all the time, should be referencing True. Every time you say, or write a bearing you should be writing T next to it (as long as it's True), and if the apocalypse has come, and you need to call SAR, and can give us a bearing, then *please* specify if it's in True or not.

There's the end of lesson 1.. I'm keeping it informal, so lets get to talking if you guys have questions about this stuff or let me know if I should just keep chugging along. Questions? Comments? Now's the time to start the discussion. If there's positive feedback here than I'll start working on Nav 102, and go into Compass types/parts, my favorites, pacing, bearings, and general practical navigation stuff for in the field..
Last edited by Lurch on August 13th, 2013, 12:00 pm, edited 2 times in total.

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forestkeeper
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Re: Nav Work 101 - Cardinal Directions and Declination

Post by forestkeeper » January 25th, 2013, 8:35 pm

:D This is really great! You really explain this in simple language, a type of Orienteering For Dummies. I can't wait for the next part. I thought the declination is 17.28 M, according to the USGS Maps for the USDA Forest Service.? Won't that 1.28 of a degree (from your rough 16) make a difference? Especially when searching for a victim or trying to locate a destination?

Will

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Peabody
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Re: Nav Work 101 - Cardinal Directions and Declination

Post by Peabody » January 25th, 2013, 10:07 pm

Thanks for doing this.
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Lurch
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Re: Nav Work 101 - Cardinal Directions and Declination

Post by Lurch » January 25th, 2013, 10:51 pm

It really depends where you're at. You can check out your declination through NOAA over HERE if you've got Lat/Longs or a local Zip Code.

Realistically you're not going to be pulling off surveyor level accuracy with a normal compass, and for the most part it isn't necessary. If you do the math 1° of error at a distance of 1 mile puts you about 92' from your intended destination. That isn't a big problem, however if you forget to declinate, or worse yet, declinate backwards and now you're 32° off from where you want to be, you're now a smidge over 1/2 mile from where you want to be!

As another note, you really need to take the initiative to research your local declination, or the area you're going to be in at least every couple years. The rough guesstimation of 16° is going to be good for about another year before it should be dropped to 15°. When I started getting into serious nav work it was about 20° here. DO NOT go by the declination scale printed on USGS quads. Those were accurate, when the map was printed, or the deviation was calculated, which could be as recent as the 90's, or as far back as the 50's in some cases.

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Re: Nav Work 101 - Cardinal Directions and Declination

Post by raven » January 25th, 2013, 11:02 pm

As Lurch said, declination drifts over time -- the magnetic pole moves. Paper maps report the declination when drawn. Gmap4 reports declination (as an option) using a current model, making it easy to check before going out the door. It reports 15 degrees 59 minutes for Portland, 15 degrees 44 minutes for Mt. Hood and 14 degrees 37 minutes for Sacajawea Peak in the Wallowas.

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forestkeeper
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Re: Nav Work 101 - Cardinal Directions and Declination

Post by forestkeeper » January 25th, 2013, 11:10 pm

:) Oh cool, thanks! I never thought of that. I guess it would be a good idea to check when the map was made. I'll check out GMap4 too. I wonder if people have become lost because they didn't figure in the declination. That wouldn't be a good thing in winter.

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Re: Nav Work 101 - Cardinal Directions and Declination

Post by potato » January 26th, 2013, 3:14 am

Lurch wrote: 10°M = 26°T

Declination East, Magnetic Least

These are the same bearings.
For me, this is a bit of a confusing way to remember it. I might start to think "the needle is pointing to the 16° mark while true north is at 0°, doesn't this mean magnetic is larger than true bearings?" but thinking about it more closely I realize that the needle is pointing toward magnetic 0°, which lines up with 16° true, so 0°M = 16°T magnetic, and magnetic is indeed smaller.

The easiest way for me to remember it is: if I am standing and facing north, magnetic north is TO THE RIGHT of true north. By understanding that concept you can figure out the math&geometry at any time.
Or you can imagine that magnetic north is somewhere near Greenland... east of the North Pole, if we looked at it from Oregon.
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retired jerry
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Re: Nav Work 101 - Cardinal Directions and Declination

Post by retired jerry » January 26th, 2013, 8:04 am

Excellent writeup Lurch, thanks

Doesn't matter what the declination is

The main reason for compass is to keep going in a straight line when you can't see the surroundings.

For example, get on ridge, see what direction a destination is, then just keep going in that direction as you drop off ridge and walk through the forest.

Otherwise, walking through forest you'll walk in circles.

Now what happens when the poles reverse? It seems like the location of magnetic North is more unstable than it used to be. During the pole reversal period, there will probably be a period where there is little magnetic field. Then, we won't be protected from particles from sun and there will be a mass extinction event :)

No - poles reverse frequently (geologically speaking) so we would see mass extinction events in history, which we don't, but there might be some interesting effects.

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Re: Nav Work 101 - Cardinal Directions and Declination

Post by RobFromRedland » January 26th, 2013, 11:24 am

This is great stuff - and well explained. I look forward to "Nav Work 102"
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Re: Nav Work 101 - Cardinal Directions and Declination

Post by turtle » January 26th, 2013, 11:50 am

Thank you very much . Please continue. Expanding the skill set is a good thing. :D
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