BWCA Navionics Boundary Waters Listening Point - General Discussion
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Yakfish
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02/18/2021 11:13AM  
Has anyone ever checked the accuracy of navionics maps to reality on the lakes of the BWCAW? I was looking at a few different lakes and there were some surprises for me. I know not to rely on gps or my phone but there was a lot more information than i thought there would be.
 
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02/18/2021 11:39AM  
I used the app a couple years ago on a trip just to double check and it was pretty close at fixing my position on the map. I also double checked a couple of depth finder readings and those were pretty spot on as well. Chewed through battery on my phone pretty quickly so I didn't use it a lot, but it was fun to play with.
 
02/18/2021 08:17PM  
It is hit or miss for lake depths. Location on a map I have always thought they are spot on.

Most of the lake depths are from old DNR maps done back when they paddled aroun d the lake with a weight and string. Gives ya an idea but lake levels have changed and mapping depth contours technology has improved since the 1940’s and 1950’s.

T
 
Savage Voyageur
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02/18/2021 10:16PM  
I have the Navionics chip of North America. It has been very accurate for lakes I’ve been on. It gives me lake depths in one foot increments. The way it works is say I go to Lake One and use my depth finder with the Navionics chip. It records the lake where I go. Then when I plug in my chip to get lake data for lake Two, it downloads my lake info for Lake One and uploads new information that someone else got to my chip. So it’s constantly being revised. This is very important for coastal waters or rivers that change depths.

Everyone who makes a map of land or water depths started with the information on the maps that were drawn by the government. They are known by USGS Topographic 7.5 min maps. They were made decades ago by land surveyors. The lake depths were done by guys with weights and a rope. They compared the maps to aerial photographs and lake depth information then published the maps. Then everyone copied this information and made the canoe maps we all use. Navionics is one of many mapping companies that have used this map information to draw maps. There is a lot of room for error when you are talking about lake depth surveys with a weight and a rope. Example is Clearwater lake. There is a sunken island in the middle of the eastern big bay that is not on any map. You can see the sunken island with Google maps. If I were to go back to Clearwater lake I would map that sunken island and then everyone would know it’s there and a revision might be made. Then take into account water levels that have changed during the original surveys way back when. Our government does revise maps from time to time, but not that much up there. It is what it is and Navionics is one of the better ones.
 
thegildedgopher
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02/19/2021 12:49PM  
It varies widely for me. I have been trolling in 40fow and it says I should be on shore, and I have had other areas where it seems nearly perfect.

Keep in mind that it will only be as accurate as the GPS in your phone -- even if the map is perfect, if your phone can't accurately identify your position it's going to take a little work to figure out. The map might show a great hump, and the hump might indeed be there, but can your GPS get you on top of it?
 
02/19/2021 01:05PM  
If you're talking accuracy in terms of putting your location on the map correctly it seems fairly accurate, at least as accurate as the gps on your phone will allow.

In terms of depth accuracy I'd say they are as accurate at the data they have allows. I've fished some lakes with no data at all, some with just the old government map data, and some with 1 foot increments. I'd say the majority of lakes in MN are mapped pretty well but lakes in the BWCA are a bit hit or miss. If they have the data they seem to be pretty accurate. You do need to keep in mind that lake levels change season to season and even month to month so if the map tells you its 15 feet but your depth finder says 14 feet don't get thrown off too badly.

I personally only use the app to find structure like drop offs, rock piles, saddles etc and it works awesome for that.
 
02/19/2021 06:01PM  
I used the app on my phone last year (three separate trips: LLC, EP16 loop; EP25 up to Knife Lake) and it works well in my opinion. You download the areas you want and then just use the phone’s GPS when in the BWCA (WiFi and cellular modes off). There are two lake depth options, Nautical Charts and Sonar Charts. The latter are data from sonar unit owners that use the Navionics chip/card in their system (and allow sounding data to be uploaded to Navionics). I have found most of the BWCA lakes I was in last year were sounded by users and these available data are sufficiently accurate, for me anyway. Going forward this will be my go to for fishing depth and general GPS navigation for the BWCA. The screenshot below show the areas I have downloaded in highlighted yellow areas (BWCA, Duluth area, Lake Namakagon area in WI).

 
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