I have noticed that when I plan a spot to fish based on my gps map then go to that spot the depth, contour etc is not accurate and sometimes not even close. For example fished Lake Erie out of Lorain Sunday and found a hump to a point in 42 FOW that came up to 24 FOW...ran out there and no hump or 24 FOW. Any ideas as to what the issue might be....map card, software update or just crappy Humminbird technology? Thanks