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Old 05-27-2009, 10:59 AM   #1
Diamond_Miner
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Question Using Topo Maps

Hello all,

I have a question regarding topo maps and declination for orienteering use.

The USGS topo maps have a magnetic declination shown on the bottom of the title block for the year the map was created. The map is shown with geographic north at the top of the page.

When using the map, you need to use the current declination. So, my question is... do you even bother with the declination shown at the bottom of the map? Is it useful or is it just a record of the declination at the time the map was made?

I'm guessing that since the map is drawn with geographic north to the top of the sheet, you only need to use the current declination in the area when using the map. (ie, ignore the declination shown at the bottom of the map)

I hope someone can set me straight on this one!

Thanks!!!

CPS
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Old 05-27-2009, 11:55 AM   #2
John H Swanson
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If the map is current, then use the declination at the bottom of the map.

Depending upon where you are in the world, the amount of change in declination varies. If you were in the tundra of northern Canada, you should be very concerned with this point.

In our neck of the woods (high peaks), the change is slow. So, if you are using a map that is even 50 yrs old, then the declination at the bottom will be okay. I checked and it is about 1 degree variation. If you prefer, you can look up the correct current declination and exchange that value for the one in the map. I use this site: http://www.ngdc.noaa.gov/geomag/

Of course the real problem occurs if you have an old map with the MN lines gridded on it and then you would need to either ignore them and take bearing off the geographic north of the map using the new declination.

Last edited by John H Swanson; 05-27-2009 at 12:02 PM.. Reason: got more data
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Old 05-27-2009, 04:10 PM   #3
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That's just what I was looking for --- it's the simple answer. Map printed geographic north, therefore use current declination, not necessarily printed declination.

Thanks for the info and link!! Now it's time to get out and try this out!

CPS
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Old 05-27-2009, 04:31 PM   #4
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That's just what I was looking for --- it's the simple answer. Map printed geographic north, therefore use current declination, not necessarily printed declination.
I must ask.... what sort of land navigation are you planning to do? While you MUST take declination into consideration, here in the Adirondacks it is generally more fruitful to primarily navigate by observation of the terrain in concert with map and compass. Your precise course in the field will be more influenced by terrain characteristics than by a degree or two of declination variation that changes very slowly over decades of time.
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Old 05-27-2009, 04:45 PM   #5
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I have a little experience hiking high peaks herd trails, a portion of the Northville Placid trail, but mostly unnamed trails in the southern Adirondacks which is closer to home in the Mohawk Valley.

I have an old GPS but I really dislike trusting anything that runs on batteries in the woods. So I am looking to take out the map and compass a little more on trips and trying to either locate myself through terrain observation coupled with the map and compass, or locating myself on a road and using the map and compass to get straight to a destination.

It's a character flaw I like to try and get the best precision out of things.

CPS
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Old 05-27-2009, 04:57 PM   #6
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I have a little experience hiking high peaks herd trails, a portion of the Northville Placid trail, but mostly unnamed trails in the southern Adirondacks which is closer to home in the Mohawk Valley.

I have an old GPS but I really dislike trusting anything that runs on batteries in the woods. So I am looking to take out the map and compass a little more on trips and trying to either locate myself through terrain observation coupled with the map and compass, or locating myself on a road and using the map and compass to get straight to a destination.

It's a character flaw I like to try and get the best precision out of things.
No problem, I in fact applaud you for your goal.

Just don't get frustrated with applying too much precision to where it has little or no effect, and where there are alternative working techniques.

The key is to study the route, then navigate it, go ahead and allow yourself to make mistakes, never let a mistake go by without learning from it, and continually practice the craft. Pay attention to every natural navigation clue you see, there are dozens everywhere. While you won't likely get very "lost" on a road, I find it far easier to lose concentration of precisely where I am on a road or trail than when I am paying strict attention on a bushwhack route.
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Old 05-27-2009, 05:02 PM   #7
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Thanks! I definately appreciate the comments.

CPS
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Old 05-28-2009, 06:39 PM   #8
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A helpful book for learning how to be an expert with map & compass.
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Old 05-28-2009, 07:01 PM   #9
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A helpful book for learning how to be an expert with map & compass.
Some guy posted this thing on traditional navigation techniques on another forum. I've heard people say it is a good read.
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Old 05-28-2009, 07:03 PM   #10
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Some guy posted this thing on traditional navigation techniques on another forum. I've heard people say it is a good read.
You study that thing, and I mean study it, and you're good to go anywhere, anytime.
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Old 05-28-2009, 09:55 PM   #11
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Diamond Miner,

At some point as you build your navigation skills and use them in the Dacks, perhaps in limited visibility conditions where you are trying to find a small target, you are going to want to head on a bearing with precision to plus or minus two degrees or so.

For that you will NEED to take into account mag declination, which is about 14 degrees in the Park.

For that reason, and to minimize the chance of conversion errors in the field, get yourself a compass with MAGNETIC DECLINATION ADJUSTMENT.

You'll pay maybe $30 or $40 more, but, once you set it to account for declination, your compass and map will always agree on 'North'.

That's a huge advantage in many field circumstances!
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Old 05-28-2009, 10:33 PM   #12
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Diamond Miner,

At some point as you build your navigation skills and use them in the Dacks, perhaps in limited visibility conditions where you are trying to find a small target, you are going to want to head on a bearing with precision to plus or minus two degrees or so.

For that you will NEED to take into account mag declination, which is about 14 degrees in the Park.

For that reason, and to minimize the chance of conversion errors in the field, get yourself a compass with MAGNETIC DECLINATION ADJUSTMENT.

You'll pay maybe $30 or $40 more, but, once you set it to account for declination, your compass and map will always agree on 'North'.

That's a huge advantage in many field circumstances!
Or....you can obtain the same advantage, and even greater advantage in my opinion, with a high quality less expensive compass without declination adjustment, by using the Map Magnetic Meridian Reference Method as discussed in the navigation article. In short, you transfer magnetic reference to be the job of the map instead of adjusting the compass. Declination reference (magnetic north) is permanently drawn on the map, where it belongs, instead of temporarily adjusted on the compass where it is subject to change as you change location from map to map.

The additional major advantage is you don't use the magnetic needle when measuring a course on the map, which means the map and compass together can be in any orientation - you will always get the same answer - even if you lay the map and compass randomly oriented on the hood of a car. It amounts to the same thing, I just feel that the map preparation method is considerably less subject to error in the field and is much faster as well. No need to find a flat spot for the map and do the magnetic orientation thing, just put compass to map and turn the dial for an instant reading while walking along. And... in preparing the map at home you get to do a little pre-trip map study as a bonus.

In the image below, the declination adjustment on the compass is set to zero. The magnetic north lines drawn on the map do all the adjustment for you.
Attached Images
File Type: jpg dec.jpg (112.7 KB, 176 views)
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Last edited by Wldrns; 05-29-2009 at 08:26 AM..
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Old 05-28-2009, 10:44 PM   #13
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Yup, set your compass to 14 degrees west declination and remember there's a bit of iron ore around here so pay attention to topography too.
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Old 05-29-2009, 11:47 AM   #14
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Wldrns,

I'm glad the magnetic meridian reference method works for you and others who choose to use it.

I'd like to respond to some points raised in your post:

- I can set my compass declination adjustment to about plus or minus a quarter of a degree, which is probably as accurate as your magnetic meridian lines drawn on your maps.

- I use tens of maps per year, often reproductions of a topo segment, in doing bushwhacks. Not having to accurately draw mag meridian lines on each map is one less activity I have to do in preparing for a hike. Also, out in the field, there is no chance I will confuse the maps' north-south lines with mag meridian lines

- Magnetic declination for a good chunk of the east, west of NH is about 14 degrees west declination, in the Whites about 16, maybe 17 further east. Unless you travel a lot, you rarely have to change the setting. And if you do, it's very straight forward using the small screwdriver device supplied with these mag. declination adjustable compasses

- I don't have to use the magnetic needle when measuring a course on the map either. in determining a bearing between point A and B, when using a declination adjusted compass, the process is the same as shown in your attached jpg but with once change. Once you set the baseplate edge connecting A to B, instead of aligning your compass dial's meridian lines with your magnetic meridians, you align the dial's lines with the maps' north-south lines. That's it! Then you put the needle in the alignment arrow and away you go.
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Old 05-29-2009, 12:41 PM   #15
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Different strokes for different folks.

I've found that what I'm most comfortable with, works best for me. Sometimes that may be what is perceived as the "more difficult" way, but everyone's mind "adjusts' differently.

I have used the map method as Wldrn's suggests and it works fine. But I prefer to adjust the declination on my compass & work that way.

It "fits" me better. If that makes sense.

Whats cool here is that we're learning two different methods to achieve the same goal.

I would add that I am most comfortable in the field when i have studied my map a lot at home before I ever undertake the hike. It gives me a "sense" of what to look for and where I am, often without having to use the map or compass as often.

Hawk

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Old 05-29-2009, 11:05 PM   #16
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Some guy posted this thing on traditional navigation techniques on another forum. I've heard people say it is a good read.
That Paul Repak guy sure knows his sh!t.

I try to practice the very same techniques.
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Old 05-31-2009, 08:35 PM   #17
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Wldrns,

I'm glad the magnetic meridian reference method works for you and others who choose to use it.

I'd like to respond to some points raised in your post:

- I can set my compass declination adjustment to about plus or minus a quarter of a degree, which is probably as accurate as your magnetic meridian lines drawn on your maps.
Whoa, I challenge you to make any practical use out of a quarter degree accuracy while navigating in the Adirondack backcountry. Yes, my lines drawn on the map are as accurate as I can draw them probably within a half degree, which is more than sufficient. We're not talking about the gnat's-ass of accuracy with compass settings or line drawing here, rather we are discussing convenient ways to navigate safely and efficiently with sufficient accuracy and by making use of practical techniques and sensible accuracy - gaining some lay of the land outdoor knowledge along the way is a definite plus. I just can't imagine that a quarter of a degree, much less a whole degree makes any real difference at all in practical recreational field navigation. Believe me, over many years I've successfully bushwhacked some pretty rough stuff over long distances and it doesn't have anything to do with reading the compass to anything like a quarter degree.

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- I use tens of maps per year, often reproductions of a topo segment, in doing bushwhacks. Not having to accurately draw mag meridian lines on each map is one less activity I have to do in preparing for a hike. Also, out in the field, there is no chance I will confuse the maps' north-south lines with mag meridian lines
I use tens of maps per year also doing bushwhacks. I have a briefcase full of virtually every topo of the Adirondacks, plus many more in a map chest for other areas of the state, and other parts of the country and the world. Every one of them where I have traveled is lined in the region of interest. For map segments that I download off internet sites, photoshop is conveniently used to draw lines on them also.

I very much enjoy drawing mag meridian lines on each map, especially in an area new to me, or areas I've not recently traveled. My philosophy is to spend considerable time at home on map study before every trip, as much as a couple of hours or more if that is what it takes for me to learn what the map and the terrain has to offer. It's amazing how much you pick up, and how much you save in the field, from extensive map study.

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- Magnetic declination for a good chunk of the east, west of NH is about 14 degrees west declination, in the Whites about 16, maybe 17 further east. Unless you travel a lot, you rarely have to change the setting. And if you do, it's very straight forward using the small screwdriver device supplied with these mag. declination adjustable compasses
True, and it's just as easy to draw a line on a map at 14 degrees as it is at 17 degrees.

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- I don't have to use the magnetic needle when measuring a course on the map either. in determining a bearing between point A and B, when using a declination adjusted compass, the process is the same as shown in your attached jpg but with once change. Once you set the baseplate edge connecting A to B, instead of aligning your compass dial's meridian lines with your magnetic meridians, you align the dial's lines with the maps' north-south lines. That's it! Then you put the needle in the alignment arrow and away you go.
What North/South lines on the map are you using? If you are using the UTM overlay grid lines, they may be offset from true N/S by as much as +/- 3 degrees. You would have to compensate your compass declination setting by this additional correction factor, and accurately adjust in the proper east or west direction.

Many of the places I go don't have updated maps with UTM grids. One case of a place I frequent has a last map update by USGS in 1943, no N/S lines at all other than the edges of the map itself. Since I don't use GPS when recreating anyway, it makes little difference whether the grid is there or not. Beavers have made the raw map almost unusable anyway.

Hey, like Hawk says, its all in personal preference. Either method works as long as you fully understand what you are doing and can operate in all conditions. I teach the map line method to guides and all who take time to try it seem to like it. I've done the compass screwdriver offset also. I can think of a couple of SAR missions in a new area where I didn't have time to print a new map. A ranger handed me a bare map and I had to do exactly this using the compass declination adjustment. It worked of course, but is simply not my preference when I have time.
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Last edited by Wldrns; 05-31-2009 at 11:44 PM..
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Old 06-01-2009, 01:03 AM   #18
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Wldrns,

I stand by my original point, the conclusion of which was the declination setting adjustment carrys about the same error as your drawn, mag meridian lines - period. I never claimed I, or anyone for that matter, can compass navigate to a precision of a quarter of a degree. But you do want MINIMAL error in each navigation component or technique you employ. For instance, say for brand XYZ, compass declination adjustment can only be set to plus/minus two degrees. In certain situations, you'd have problems in the field for sure.

When taking everything into account, I think the best compass users with the top notch compasses are good to about plus/minus one to two degrees.

I mainly use the USGS Adirondack Park, 7 by 15 minute, 1:25000 metric series maps, where Grid North typically ranges from less than half a degree to almost one degree, which in my experience can be ignored. If Grid North was more than a degree off from True North, then I would reset my declination adjustment accordingly.

If you have one or more handy, please specify which maps in the above series have grid lines that are offset by 2 to 3 degrees from TN - I'm not aware of any.

As I do not use software processed maps or mapping systems, all my maps are old fashioned - they have the grid lines printed right on 'em. What a concept!
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Old 06-01-2009, 09:53 AM   #19
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Wldrns,

I stand by my original point, the conclusion of which was the declination setting adjustment carrys about the same error as your drawn, mag meridian lines - period.
I have no argument with your original post, other than one does need a quality made compass, but it does not need to have mechanical declination adjustment to be an accurate aid to navigation. I point out that other just as accurate methods are available which may enhance overall understanding of navigation techniques and terrain passage. However, as they say, the practice of "measuring with a micrometer, marking with a felt tip pen, and cutting with an axe" doesn't gain any additional practical real-world accuracy. There's a whole world more that goes into precision navigation than the couple of degree accuracy of a compass.
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When taking everything into account, I think the best compass users with the top notch compasses are good to about plus/minus one to two degrees.
I agree with that.

A story that many air navigators have heard and often done (including myself):
"Pilot this is the Nav. I need you to come right one degree".
Pilot: "I can't come right one degree, the autopilot wheel is not that accurate".
Nav: "Ok pilot, then let's come left 2 degrees."
Pilot: "Roger, coming left 2 degrees".
brief pause....
Nav: "Pilot, turn right 3 degrees".
Pilot:"Roger, 3 degrees right".

Quote:
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I mainly use the USGS Adirondack Park, 7 by 15 minute, 1:25000 metric series maps, where Grid North typically ranges from less than half a degree to almost one degree, which in my experience can be ignored.
This seems in conflict with your earlier statement about minimal error.

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If you have one or more handy, please specify which maps in the above series have grid lines that are offset by 2 to 3 degrees from TN - I'm not aware of any.
Maximum grid convergence deviation from true north occurs at the 6-degree zone boundaries. In the continental US this grid convergence declination difference can be as much as 2.5 degrees, up to 3 degrees a bit farther north. For example, the Barnet Vermont 1:25000 topo map is on the 72 degree longitude zone boundary. From the map legend, UTM Grid Declination is just over 2 degrees east (vs a magnetic declination of 16 degrees west). So you would be in error by 2 full degrees by measuring from UTM north lines on that map.

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As I do not use software processed maps or mapping systems, all my maps are old fashioned - they have the grid lines printed right on 'em. What a concept!
Some of the "latest" maps you can get are even more old fashioned than you think. Not all have grid lines printed on them. Look at those for the Tug Hill plateau, just west of the Adirondacks. Look at the maps of Sears Pond and Page. I don't care if you buy the paper from USGS or download a soft copy. The most current update was in 1943. There are no grid lines or other "north/south" lines at all. The only N/S line is the edge of the map, which by definition is TN. My copies have magnetic N/S lines hand drawn on them for ease of navigation.
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Old 06-01-2009, 10:26 AM   #20
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MAP FIGHT!!

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