Magnetic Declination (very) simplified

[@DylanAnderson-j5c]

As a student taking an MS course in Geodesy, you do a very solid job of distinguishing the reality of magnetic declination. Thank you.

[@mariozavood]

Great video. For quick error calculations, which can be (fairly) easily made in your head, pilots use the 1:60 rule. Check it out. It is basic an application of sin(x) ~= x for small x, where x is in radians. And since 1 radian is around 57 degrees, which is close enough to 60… In any case, I could quickly calculate that your error was something around 1250/4, plus a bit, I.e. 320, before you were able to even get out your calculator. 😊

[@vayde]

Thanks for this!

[@redf7209]

?????? not a clue what you mean

[@mariozavood]

@@redf7209 trigonometry…. Just a quick mental arithmetic shortcut for calculating the value of sine or tangent of small angles. Basically sin x and tan x are almost equal to x/60 where x is in degrees and the angle is below 15 degrees.

[@redf7209]

@@mariozavood Ok I get it now, I knew deviation for that small angle is essentially tan x or sin x by distance but I just couldn't relate what you were saying to that.

[@ezekielbrockmann114]

That's the most British thing ever: _"Well I haven't had tea for @__2:11__, so I'm going to have to stop filming now and make a cup."_

[@N7VAN...]

Great video. Probably the simplest I have found so far on KZbin.

[@TheMapReadingCompany]

Great to hear!

[@alanedwards8239]

OS maps include the annual change so you can work it out at GZ. I've just tested it on a 2014 Explorer against the BGS website and the answer is virtually the same. Back in the day when I started using a compass there were no computers or phones so we had to do everything manually :-) . Great video as always

[@redf7209]

need to have an upto date map as things as rate and direction change

[@TDG-s7g]

Hello from Wyoming, USA. I just found you and I've subbed. Thank you for the exellent teaching!

[@TheMapReadingCompany]

Thanks for subbing!

[@luky46]

Thank you for your video . They are extremely useful, after your video finally I can use properly my Commenga.

[@TheMapReadingCompany]

Have a look at this video. kzbin.info/www/bejne/q6vLhZRjatd8e9k

[@Throughthelookingglasss]

Thank you so much for this simplified video. Most people like myself from the city are looking to get into navigation no idea what most of the Compass and map terms are, you explaining the terms in an easy descriptive way, was awesome. I haven’t been able to follow along with a beginner video as well as this one, well done.

[@TheMapReadingCompany]

If you are new to navigation you could watch the videos in this playlist which I made a while ago. kzbin.info/aero/PLtmTvvlTrlahCoV4mgSzG6s_gF4xLLUU_

[@Throughthelookingglasss]

@@TheMapReadingCompany amazing thank you !

[@charlesmckinney]

I was taught LARS law in the military. Works as well today as it did 54 years ago.

[@TheMapReadingCompany]

The old style Left Add, Right Subtract is the same as Grid to Mag Add, Mag to Grid Get-Rid. The problem with that is it relies on you (the navigator) being in an area which is to the west of the agonic line and this changes all the time. A prime example of this is that the whole of western Europe, including the UK, used to be the west of the line, but now, as the magnetic north pole continues its progression towards Siberia, much of it is now to east of the line and all of it will be within a few years. So Lars will no longer work here. The method shown in the video will work anywhere, regardless of which side of the line you are.

[@tonyb1984]

​@@TheMapReadingCompanyAbsolutely correct 👍🏻👍🏻

[@gordonmiller4439]

@@TheMapReadingCompany Left Add, Right Subtract (LARS) works with either a westerly declination or an easterly declination. LARS is simply based upon looking at the declination diagram. Draw a westerly declination diagram on a piece of paper. Under it write: (left) Grid to Magnetic = Add (looking at the diagram you are going left from GN to MN) Under this on the next line write: (right) Magnetic to Grid = Subtract (looking at the diagram you are going right from MN to GN) Draw an easterly declination diagram on the same piece of paper. Under it write: (right) Grid to Magnetic = Subtract (looking at the diagram you are going right from GN to MN) Under this on the next line write: (left) Magnetic to Grid = Add (looking at the diagram you are going left from MN to GN. It really is simple and all you need to remember is to look at the diagram (whether westerly or easterly) and apply LARS. I thoroughly enjoy your videos and especially the waffling! All the very best, Gordon

[@wilsonmicallo]

@@TheMapReadingCompany I'm really new to navigation, but I can't understand why do we need mnemonics: in my mind if declination is 3deg East it means the compass will point 3degs east, so I should rotate the gear 3deg eastwise (it's pointing north, since it's still on the map, so rotate eastwise is the same as subtract, but I'm visualizing it so I'm sure not to get the wrong direction) What I'm missing here?

[@jimboase5005]

Just a comment; when in the Navy (navigating) the difference between True North and Magnetic North was called Variation and was marked on charts. Deviation was the additional change in compass direction resulting from magnetic effects of metal in the vicinity of the compass. Declination was completely different and refered to how far the Sun or Moon was North or South of the plane of the ecliptic (e.g. the Sun would apparently move 23.5 degrees North and South during the seasons; solstice etc. ) When I went flying the charts also used the term 'Variation'. This is only a comment for information and not criticsm. I am a fan of your videos

[@TheMapReadingCompany]

Hi Jim, thanks for that. I didn't know that about naval navigation terms - every day is a school day

[@zooknz1711]

I was taught the same when I learned to fly in the late 70s. I also enjoy these videos.

[@P6009D]

I understand that you simplify the concepts. If I have a declination of 10 degrees to True North and also an angle between True North and Grid North of 5 degrees. Then my correction will be 15 degrees to get what you call the Grid Magnetic angle. The problem is the following: Some Civil maps have no information about either the Declanation or the Grid Magnetic angle. The only possibility is then to look up the Declanation and turn the house in Meridian direction on the map.

[@TheMapReadingCompany]

Could you tell me why in North America and Great Britain the magnetic declination is adjusted to Grid North (GMA, Grid Magnetic Angle, delta 𝝳 ± omega Ѡ) while in Western Europe we always take into account the magnetic declination adjusted to Geographic/True North (delta: 𝝳). In my opinion it seems more logical to use GMA since we work on a map but... In practice two people could end up in different places with the same azimuth and this would be a nonsense. I would really appreciate an explanation as simple as posiible please. Thanks in advance Hi, thanks excellent question. As you know there is Magnetic North which is where your compass needle points to. Generally this is towards the magnetic North Pole but on a smaller scale your compass needle actually points in the direction of the local magnetic flux lines. There is also True North which is the place at the top of the axis about which the Earth rotates (the North Pole). Lastly there is grid north which are indicated by the vertical lines on a map. These are not parallel due to maps being a projection and being flat (2D) but representing a globe (3D). You can imagine three arrows heading away your location to these three “Norths” which each arrow pointing in a different direction. The angle between Grid North and Magnetic North is called The Grid Magnetic Angle. The angle between Grid North and True North is called Magnetic Declination. So back to your question: The reason why most people (in all countries) use the Grid Magnetic Angle rather than the real Magnetic Declination is quite simple. True North lines are not shown on the maps, so they have to use the grid lines as that is all there is.

[@brucefay5126]

NOAA is the “National Oceanic and Atmospheric Administration.”

[@Aldoleapold]

Would enjoy the methodology for working out error distance. Am a Forester here in States. Finding survey pins and so forth. It would be helpful to know. Enjoy your presentations Cheers

[@TheMapReadingCompany]

Hi Sam, I just post posted a video last week on how to calculate error distance. Is this what you're looking for? Hope this helps. Here is the link to the error calculation video kzbin.info/www/bejne/omTMmaqDdt1qjsk

[@lew5268]

I enjoy very much your presentation method. (The information id of course very helpful). Lew; USA viewer

[@TheMapReadingCompany]

Thanks Lew.

[@spdaltid]

Thanks for the disclaimer, I've always refered to it as Variation.

[@chrish6171]

Great video, I have a question- if my GMA at the moment in the uk is 1 mill westerly and the accuracy of a compass is +/ -20 mils then there would be no reason to apply my GMA correct? But I would need to work out what my individual compass error is and apply that?

[@higherfordkid1625]

In my marine training we called it magnetic variation. On top of that we had problems with compass deviation, so the calcs were more involved and the charts were aligned with true north. Why is your grid north not aligned with true north, as in the picture ? To what is it related? Thanks for a neat video.

[@troglokev]

UTM is commonly used for map grids. It projects position on the geoid to a point on a cylinder that intersects the geoid along the longitude at the middle of the UTM zone. The grid lines are parallel lines on the cylinder. If you project a line of constant longitude onto this, it will be a curve. The difference between this curve and the grid lines at your map’s longitude is the difference between true north and grid north. Google for “grid convergence”, and you should be able to find a bunch of useful resources, including helpful diagrams and web sites that can calculate it for you. If you want to hurt your brain, Google “Redfearn’s formula”…

[@matthewpolo227]

@9:04..."IF YOU USE A COMPASS TO TAKE A COMPASS BEARING DO THE OPPOSITE" ..WHAT DO YOU MEAN BY OPPOSITE ?

[@TheMapReadingCompany]

Hi Matthew, thanks for joining the conversation. For Compass to map you do the opposite of what you would do for Map to Compass. The reason for this is that if you take a bearing from a map you will have what is known as a TRUE bearing - so your bearing is in relation to where the vertical lines on the map converge, at the top of the earth (I may do a video on Mercator map distortions when I have time 😊). But, if you take a bearing using your compass it is a MAGNETIC bearing which has relationship to where the magnetic North Pole is currently - which in most cases is different to where your map (north) points. So when swapping from one to the other you’ll need to make adjustments. So:- If you take a bearing from a map and you have a WEST declination you ADD the amount of declination to the bearing. If you take a bearing from a map and you have an EAST declination you DEDUCT the amount of declination from the bearing. The opposite is done if you use a compass to take a bearing and use it on a map. If your area’s declination is WEST then DEDUCT the amount of declination from the bearing before you use it on a map. If your area’s declination is EAST then ADD the amount of declination from the bearing before you use it on a map.

[@matthewpolo227]

@@TheMapReadingCompany THANKS FOR REPLYING...BEGINNING TO UNDERSTAND BUT WILL HAVE TO CONTINUE TO WORK ON IT. THIS IS MY FIRST COMPASS.

[@andreafedrighi495]

@@TheMapReadingCompany But if I set the declination correction on the compass beforehand (e.g. Suunto Pro...) can I ignore these corrections that you say you are making? Are they valid equally, reciprocally, from map to real and from real to map, always without further corrections?

[@markthomasson5077]

I always thought grid was true north. Of course I am a sailor, so this I believe/ hope! is true for marine charts. Just looked this up. Grids are true 1k squares, starting on the prime meridian, so the further west / east and north you are, the more grid deviates from true north. But as it is not much, it isn’t worth being overly concerned about.

[@TheMapReadingCompany]

It depends on where you are. True north points to the place on earth where it spins on it's axis. Grid north points along the vertical lines on your map.

[@spdaltid]

@@TheMapReadingCompany Wouldn't that would depend on the type of map projection? Also, I have flown quite a number of polar flights and followed along with Grid North and a [azmiluthal projection] Grid North Plotting Chart. It is an interesting exercise when passing closely abeam the Geographic North Pole. The closest I ever passed crossing the Prime or 180 was 60nm south [89N] of the pole. Only When crossing the 0 [ Prime] or 180 [Antimeridian] do the vertical grid lines point to True North. This varies, such that when crossing 90E or 90W, the E-W horizontal gridlines align toTrue North.

[@ryanbeard1119]

So do you comp your comp the bezel, or use the declanation scale lines, and lining g these up with you north guide lines. Then dray your bearing line, I'm confused

[@Macro-photographer]

Instant sub for making it uncomplicated

[@TheMapReadingCompany]

Thanks for the feedback Graham

[@timothykeech7394]

It would have been useful if you had shown how you set your direction of travel physically by using the compass needle pointing to magnetic north and showing the resultant setting after the calculations. You've probably done this on another video but it could have finished up this one nicely. I have only just found your you tube site so I have not seen all.

[@gammpajka]

If meridian convergence is 1.2°E and magnetic declination is 7,85°E, am I stupid if I subtract 1.2 from 7.85 and adjust only 6.65° ?

[@TheMapReadingCompany]

As soon as you walk east or west the convergence will change. So the best idea is to just use grid north. As the declination is E then you subtract it from the bearing if taking it from a map.

[@Thatcanadianguyehh]

NOAA shows a declination of -16.7. Do I adjust E or W?

[@simonmcowan6874]

When I was in the army it was simple, Mag to grid, get rid Grid to mag, add.

[@TheMapReadingCompany]

Me too when I learned. The problem is that (as the MNP has moved) Mag to Gid, etc. doesn't work anymore in the UK

[@Robert32571]

Good morning, Since the declination is indicated on the maps, what credit can be given to this data when the magnetic north changes significantly in a few years? The renewal of French maps is non-existent, so I cannot trust the variation they indicate. Can you confirm or qualify this point? Thank you so much

[@TheMapReadingCompany]

Hi Robert. I can’t comment on French maps but I do know that OS (British) maps are updated very regularly.

[@jenhamilton]

I sorry if this has been asked before. I looked down and didn't see it. Couldn't you align your map to magnetic north without adding or subtracting degrees?

[@TheMapReadingCompany]

A map is drawn using ground features on a grid which aligns (approximately) towards the north pole. Your compass, in most areas of the world, lines up with the magnetic north pole. So if you're going to set a bearing on your compass and then follow it, the direction your map is pointing whilst you're taking you bearing from the map makes no difference.

[@jenhamilton]

@@TheMapReadingCompany I am sure that I am missing it. Lets say you turn those grid lines (the map) towards magnetic north (using compass) haven't you removed declination from the equation by just using MN as 'north' instead of what the map wants? Thanks for the response(s) A chosen azimuth based on the landscape wouldn't care what way your map is turned...but I am having trouble understanding why this wouldn't work. ....I guess I'm talking about orienting the map to the landscape and using MN as the guide. I watched your trig video about error in wayfinding..very interesting.

[@wonton8983]

I don't know why I'm here, i have no knowledge of compass use or orienteering but youtube recommended it. However, i'm a think outside the square type of person and your suggestion of just turning the map to align with magnetic north sounds feasible to me.@@jenhamilton

[@elizaalmabuena]

Not quite, here goes my attempt to explain. Go ahead and orient your map to Magnetic north, set your compass up to take a bearing from point a to b on the map. Once you have that bearing leave your compass on said map position and shift the map around a bit.... the bearing stays the same. Shift it some more, stays the same. See the issue now? On the other hand, If you could use landmarks to orient your map's north and then compare that to the magnetic north of your compass you might notice a slight discrepancy. In such a case set up the compass to take the bearing and adjust for that discrepancy by adding or subtracting degrees until the magnetic north of the compass aligns with the map.... now you adjusted said magnetic declination you were skipping before. Makes sense?

[@johncooper3171]

Hi I did a BGS ON GRID SK 127 874. It came back with Magnetic north is estimated to be 0 deg 18 min west of grid north (British National Grid) at this location in July 2023. Does that mean the Declination is 0 deg ? Thanks Jc.

[@TheMapReadingCompany]

Hi John, this video was filmed at SK 25138 80533 (not Nether Tor - although another video was filmed on the other side of Grindsbrook Clough from there kzbin.info/www/bejne/ZqvFdHiOn8Rlb7cfeature=shared). With a hand held compass it's not possible to walk on a bearing of less than around 2 degrees over uneven, craggy ground. So yes you can assume it's zero.

[@munchgo2834]

I Google my location, and google say is In Cebu, Philippines Declination is -1.59' , declination is Negative ( west) ...how would I do this if I go bearing 301deg...

[@clivenewton7609]

Here in the U.K. using a silva Expedition 15(?) compass there isn’t really an issue at the moment, we are dealing with minutes of angle (11 min. East July 2024)😂 bearing in mind also the illuminated index mark is at least 2 degrees thick!!! If memory serves, in all the years I’ve been messing with M&P the most I’ve had to add was 6 degrees 😂😂

[@davidcousins3508]

Am I correct in thinking that the OS maps show the declination at time of publication with yearly adjustments to be made ?

[@TheMapReadingCompany]

Hi David, yes OS maps show the declination at the time of printing and the expected yearly change.

[@coleparker]

Two things, check the map date at the bottom, declination changes a full degree every year a general rule, second, be aware that the magnetic north is shifting faster now than in the past. Finally before going out, check with a govt web page where you can find out what the latest declination is.

[@TheMapReadingCompany]

Hi Cole, according to the BGS at the moment in the UK (I haven’t looked at other regions) the mag declination, moves approx. 25km per year. So that would be a change of about 1 degree every 5 years. As you say this may change as it seems to be speeding up.

[@coleparker]

@@TheMapReadingCompany I am probably wrong in my calculations. According to the calculator I use, in the western region of the US (specifically California) the annual rate of change is approximately +/- 5' each year. So that would make it 30' minutes every 5 years and a full degree every 10 years if one degree is 60 minutes. As for the speed up I got this info from a scientific article on Magnetic declination rate of change. This has concerned me only because many of the archaeology sites I recorded are mapped to the declination that was present at the time. BTW, great discussion. I am learning a lot here. 😊

[@TheMapReadingCompany]

Hi Cole You’ve made a good point. Here’s a thing: your compass does NOT point at the magnetic north pole - yeah I know all the website and videos will tell you it does (and they’re written by “experts”? - I’ve even seen this on university websites, which is a shame as they really are supposed to know). Your compass actually points in the (horizontal) direction of the of the local magnetic field. This is reason for (in some areas) the needle of your compass pointing in some very strange directions when compared with a direct line to the magnetic north pole.

[@tedmarz7856]

It is actually a little worse than that. This from sailing navigation. You will also have compass deviation to have to consider. As well as grid reference to mag north declination and any locally induced variations ( e.g., iron ore deposits). For a hiker compass variation probably isn’t a big issue. For a sailor jaunting around in a metal structure it can be.

[@coleparker]

@@tedmarz7856 Totally agree. That is why one needs to study those variations before starting out, if one is going to rely strictly on compass.

[@redf7209]

Just curious, you are standing beside a very large lump of sandstone held together by Iron mineral. Did this cause any compass anomaly?

[@JackAlford]

My OS map is from 2019 and highlights an annual change of 12’ with it now being 2024 how do I calculate this? Would really appreciate the help 🙌🏼

[@TheMapReadingCompany]

Just for you Jack: kzbin.info/www/bejne/ioesiYiQqKZpadU

[@ryanbeard1119]

So the error comp math is just right angle trig, having dividing the total error to get a right triangle, or as you state Arc of Circle.

[@colinremmer2417]

Which website would you recommend for the declination in France? Thanks

[@TheMapReadingCompany]

www.magnetic-declination.com/

[@colinremmer2417]

Thank you@@TheMapReadingCompany

[@wictimovgovonca320]

I just set the declination on my compass, and it looks like the one you are using here supports that. If I am out walking for a day I will be using only one (or two adjacent) map and the declination will not change for that walk. No math needed.

[@TheMapReadingCompany]

Yes. If your compass has a semi-permanent declination adjustment you can just set it and leave it. BUT This is ONLY when taking a bearing from a map and using it on your compass. If you take a bearing with your compass and want to use this bearing on a map you must reset the compass and do the opposite of the declination. See here kzbin.info/www/bejne/ipeco6WjppqJnJo

[@ibeattheleaves5005]

How do you find navigation maps? I'm finding classes and groups but no maps.

[@TheMapReadingCompany]

I would suggest a map with scales or around 1:24,000 or 1:25,000 are the best for walking in the hills. I get my maps from the UK Ordinance Survey shop.ordnancesurvey.co.uk/maps I have also bought a few US Topo maps from here as they will post to the UK ngmdb.usgs.gov/topoview/viewer/#4/39.98/-100.06 It depends where you live as to where you buy from

[@ianbarnett]

This seemed to end abruptly… left hanging on your final question? Is there some missing? Would have been good to point out the lay of the land and orient your map and compass with the land?

[@YourLifeWasting]

But wouldn't you subtract the 15 degrees of a west declination to go from a magnetic bearing to a grid bearing? Or are you just adding to 15 degrees to get a magnetic bearing and your not taking a grid bearing?

[@TheMapReadingCompany]

At 6:20 in the video, I'm using a Grid bearing going to a Magnetic bearing - so (as it's west) I add the 15 degrees.. I hope this helps.

[@YourLifeWasting]

@@TheMapReadingCompany This does clarify things up for me thank you

[@terrystephenson984]

I’ve watched quite a few of your videos, and giving them all 👍. I have a very good understanding of how to correct for magnetic declaration. I live in San Diego,CA and my declamation is 11° easterly, so I know that I have to add 11° when taking a bearing with my compass. The part that I just can’t quite work out is why I need to subtract 11° when taking a bearing from the map to the compass. Can you shed any light on that? Thnx

[@coleparker]

Well, magnetic north in California is east of True North. So you subtract 11 degrees to get True north bearing or add to get your magnetic bearing if that is what your are aiming for.

[@TheMapReadingCompany]

Hi Terry - good question. Remember that East is positive and West is negative. As you live in an area where the declination is 11 degrees East this means that your area is positive e.g. +11. If you lived in an area with 11 degrees West this would be negative e.g.-11. Both of the above, + or -, are relative to true north. So at the moment you are taking a bearing “with a compass” from a terrain feature so you’re adding the 11 to the compass bearing to bring it back to true north. When you take a bearing “from a map” you need to subtract it from the map bearing, again to bring it back to true north. I hope this helps

[@terrystephenson984]

@@coleparker actually magnetic north in California is east of true North, which is why I have an easterly declination.

[@coleparker]

@@terrystephenson984 You are right. I had a mind f*rt when I was writing my comment. Part of getting older ( I am 70 now on my way to 71) I think I corrected it.

[@snuffle2269]

I dug out an old map and page I wrote up for magnetic declination in Lithuania 2007. My has it changed thru 2023. Don't get me going on the Pole Shift coming up.

[@SabcatPrinting]

Its just like with nuts and spanners… lefty loosey, righty tighty… or is it the other way round? 😉

[@NancyRode-u9i]

👋 thank U

[@kennethlapointesongwriter3330]

Sure. West is best (add)...East is least (subtract)...when going from map bearing to compass. And the opposite going from compass bearing to map.

[@Senseigainz]

1:60 rule of thumb for the error calculation

[@mikefule]

Good video. The actual declination where you filmed it is negligible. 0 deg 2'

[@TheMapReadingCompany]

Thanks for the feed back Mike, yeah you're spot on 0.2 - but saying there is no decilination wouldn't have made a very interesting video.

[@Sparky-ov1ot]

Well did you get there ok? Enjoy how you keep things simple, I want to spend my time walking not doing maths.

[@dasfahrer8187]

Link to the Error Calculation video is dead BTW.

[@TheMapReadingCompany]

Thank you for letting me know. I have updated the link.

[@westbsa7424]

👍👍👍

[@412fk]

What happened, did he make it?

[@TheMapReadingCompany]

Yes :-)

[@mihailvormittag6211]

👍

[@georgen9755]

I taught environmental engineering ,

[@raystewart6524]

Grid to Mag ADD Mag To Grid Get Rid..

[@AlexeiMasterov]

Sending people to google for something that you are trying to explain is a dirty trick.

[@TheMapReadingCompany]

I don’t know where viewers are, so if you use Google to search for your local declination you’ll get much better (worldwide) information that I can supply.

[@alangordon3283]

It’s nothing of the sort.

[@joshuabradshaw5270]

I-so-gonic. It's an isogonic line. adjective GEOGRAPHY indicating or connecting points of the earth's surface at which the magnetic declination is the same. Translations and more definitions

[@TheMapReadingCompany]

Hi Joshua, sorry for the confusion. I have discussed the "isogonic" line in another video. Let’s say you live somewhere with a declination of 5 degree west. Further north and south of your position the declination will be the same. All the places will the same declination are said to be on an isogonic line. In this video I was discussing the "agonic" line, which is an imaginary course covering all points in which the magnetic north and true north are the same.