All,

I am nearing the start of this summer's trip and beginning to pack things. We leave Friday morning. We have purchased both the Fisher and McKenzie maps for our route. We also received the National Geographic maps as a gift a while ago. The Fisher map is F-10. I was looking at it today while getting ready to slip it into our map case and wanted to set the magnetic declination on my compass. I realized that I can't find anything regarding declination on this map! Both the McKenzie and National Geographic maps are very clear about the declination.

Do any of you know if I'm just overlooking something here? I checked the front and back of the map several times with no luck. I also checked the Fisher website and came up empty.

Appreciate any help you can provide. The declinations are so minor in this area that worst case scenario I will just leave the compass setting at 0 degrees.

-Kendis

Current declination for F-10 would be about west 1.5 degree. Hardly enough to worry about. There are some magnet anomalies in the BWCA due to iron content in the bedrock, but that has never caused me any trouble though I have seen some odd compass behavior occasionally. I basically use the compass to orient the map and keep track of where I am on the map all the time.

Declination changes so it's best to update it every few years. Since many people keeps maps for a lifetime it could get you into trouble using one printed on an old map. It's not a huge change but for Brule Lake for example it's about 1° every 10 years.

Declination is specific to the area, not the map. If you have it marked on one map in one spot it will be the same on the other maps in the same place. Given where the BWCA is though, it's very minimal anyway. If you were directing artillery fire it would be a big deal - if you are trying to find the next portage, its not a big enough deal to worry about. I would never go up there without a compass, but I bet I only use it on one out of every 5 trips or so - and then only for one or two situations.

I checked my own Fisher maps for the last ten years, and I don't see declination indicators on any of them.

Because I enjoy this sort of thing, I wanted to see if I could independently verify the declination findings cited above.

According to the BWCA.com lake maps pages, Brule is located at latitude 47.943 and longitude -90.692.

Entering these figures into the nifty NOAA Magnetic Field Calculator, I find that the declination as of today is 2.45 degrees west. The annual change is .04 degrees west, which means that it increases by 1 degree every (1/.04) = 25 years.

Results for Wood Lake, in the center of F-10, are somewhat different. Declination is 1.67 degrees west, with an annual change of .05 degrees west, for an increase of 1 degree every 20 years.

Set your declination adjustment to 1.5 degrees for this area, and you should be good to go. Note that careful use of an orienteering compass can give you accuracy to about 2 degrees, which equates to about 50 yards at a distance of one mile.

I hope that helps. Corrections are welcome if you spot an error.

To answer your question, what you are missing is these maps are not always accurate. Older fisher maps say right on the map, “This map is not intended for navigational use, and is not represented to be correct in every aspect”. Newer fisher maps read “Reviewed for accuracy by the Forest service USDA”, then a date of review. Translation is every newer BWCA map was copied from the government surveys when they mapped the areas. They add campsite and portage info and sell it to us canoeists.

All of the map information on land topography or lake depths used in every maps us canoeists use was taken from an original USGS 24000 7.5 min topo maps charted from the land survivors. Fisher didn’t survey the area, our government did.

Fisher maps cover a general area us canoeists like to travel. The USGS maps cover the entire United States. The same are on a fisher map will take two or three USGS maps. Fisher maps don’t give too much information about declination or coordinates because of the map scale they use. Fisher maps give us what we need, campsites, Lake and portage information. Declination on a real map is accurate because the map is accurate. Us canoeists don’t really need a super accurate map to navigate around the area because most of us just travel by lake only and not wide open areas. The declination varies a bit up there and is about 1/2 to 1 1/2 deg West if I remember right depending on where you are. On a lake this number is within the error zone of your navigational skills and your compass accuracy. In other words don’t worry about declination.

sedges: "...
There are some magnet anomalies in the BWCA due to iron content in the bedrock, but that has never caused me any trouble though I have seen some odd compass behavior occasionally.
...
"

This is reassuring. My compass, newly purchased on the way to the BWCA, was about to go back to REI because it wasn't consistently pointing N during my trip.

Go with your plan of just ignoring it for that reason and all the ones already mentioned. If you get lost up there, it won't be for that reason - it'll be because you forgot to stay found :).

If you want to make a notation on your maps of the magnetic declination, you can use this interactive map tool to zoom in on any point you wish to determine the declination:

Interactive declination map