lake map question

I recently bought a H20c with a Navionics premium north chip. I used it on Pokegama and Moose Lake near Grand Rapids Minnesota. On Pokegama the map was off as much as 4-500 yards. I would be on shore on the cabin deck and it would show me way out in the lake yet. I would be on one side of a big island and it would show me on the other side. These are just 2 examples. If I swithed off the Navionics mode and went back to the lowrance mode with the lakes roughly shown it would show me on the lake a LOT more accurately. I was told this was normal ,on another forum, because Navionics was probably using inaccurate info on those 2 lakes since they weren’t the major lakes like Leech, Mille Lacs, etc. Is this true or do I have something wrong with my chip. Pretty disappointing if they only have accurate mapping on the few major lakes. They should tell people wwhich lakes are accurate and which ones aren’t if that is the case. On Moose Lake, I was driving 100 yards to the south of a big rock pile in deep water and it showed me driving right over the 4′ depth of the middle of the rockpile.

First of all Welcome to IDA!

Secondly, very good question. I believe Navionics does tell you the level of accuracy of each of the lakes on their chips. CLICK HERE and I believe they tell you waht level every lake is. Your problem is common depending on the lake. I was up on Namakan and the whole lake was pretty close utnil I got over by Sandpoint. Then it was off like you talk about. I was driving through the middle of the island on the map, but was in 30 feet of water????? Wade from Jolly Ann Marine will answer your question a little better when he sees this post. There are different levels of definition. Some of the maps on the chip are I believe just taken off the DNR maps. Other ones that have 3 and 1 foot contours or High Definition maps were actually plotted, etc.

The Pokegama map is WAY off and basically worthless as you have seen. I have a cabin in grand rapids and Pokegama is one of my favorite lakes. Still have to do it the old fashion way out on Pokegama.

Eric Ahlstrom

Like the guys said above, there are various levels of detaila nd accuracy depending on the map data source for the specific lake. There a some maps on the chip that are off quite a bit. The best thing a guy can do in that case is to file a Discrepancy Report .

Navionics does offer soem information on their website that can help you determine the level of detail for a specific lake. The best maps will always be the “survey maps” which are listed in red on their website. Other lakes maps that tend to be very good are the lakes listed as FHS lakes and Lakemaster lakes on the lake list. Over time, we’ll eventually see many more of our favorite lakes being surveyed but it is a time-consuming process, so in the meantime, they will continnue to use the best or only data source available.