I will second the LakeMaster chip. They have the contour lines every 5' down to whatever the depth of water you are in. You will see the underwater structure that is below 30', where Navionics chips contour lines end. Also you will be able to zoom in a lot closer and can see the countour lines when zoomed out further also. LakeMaster also sems to be more accurate than Navionics. I still wish that the GPS manufacturers would have a map correction feature you could use to correct maps while out on the water.

You would be surprised at all of the structure you can find with contour lines every 5'. I have both the Navionics North and Wisconsin LakeMaster chip in a LCX-25c and always end up using the LakeMaster chip. You will really like what you see on your screen on Lt. & Big Bay de Noc's with a LakeMaster chip. I fish there often throughout the year. Have not been there much this year though but from what I have been reading on the forums, not much doing for walleye so far this year.