Can anyone tell me how Navionics sets the elevations on there HD lakes each year? I am particularly interested in Lake Oahe. My 07 chip is now pretty outdated with the rising water. I'd like to buy a new chip for 09 but would like to know what elevation the map will be based on. Thanks!

In reservoirs typicaly elevations or contour depths on charts are shown at "full pool". So your contour depth indicators will not be right most of the time. Reservoirs are rarely at full pool. Elevations on these reservoirs change every day so it would be impossible for Navionics to pick the correct depths for any given "year". But the contours should be accurate and the depth "offset" consistent.

I wish that were true. My 07 chip is setup with pool elevation for that year. Right now, with the water increases we've seen, I have no charts in anything shallower than 15' or so. This is an HD lake, so maybe they set those per year. Other lakes on the chip are set at full pool, some simple math and I am good to go.

I see your problem more clearly now. Your issue is with shallow water ( dry land at mapping time)
I know Navionics has there own mapping equipment and does actually map certain lakes, (as opposed to just using govermant survey data) on others. This is what they market as "HD".

I would have thought on these HD lakes that knowing at the time of mapping it was not full pool that they would have also used the available goverment data for the portion of the lake they could not reach with there equipment (boat) at mapping time to make a morre complete map.

Can anyone tell me how Navionics sets the elevations on there HD lakes each year? I am particularly interested in Lake Oahe. My 07 chip is now pretty outdated with the rising water. I'd like to buy a new chip for 09 but would like to know what elevation the map will be based on. Thanks!

offset your transducer to the new lake level but dont forget to change it if you go somewhere else

;)

I understand their HD surveying and the fact they probably don't have the data for the higher water other than the government surveys. I think I am just going to shoot an email to then and see what they say. I have got to get something different because right now the chip isn't really doing much for me at those shallower depths.

Unfortunatley there just is no one mapping chip that covers every lake "the best".
Different companies focus more on some lakes and areas than others. Just the nature of the beast. Fortunately with the Lowrance HD units the "base Maps" that are pre loaded are very good. So if there is not a chip to enhance the area I am working I still have a good map.
The subject has gone round and round on here but I personally think the HD is a good value over the non HD for 200 bucks, but thats just my 2 cents....
Good luck.