My experience is the basic maps that come with Lowrance units suck at very best. The navionics maps I have bought are marginally better. I feel that 1 foot contour intervals is a minimal requirement for a map chip that you have to pay extra for. I have a Great Plains Mapping chip which is excellent detail for Kansas and Missouri Lakes. It has 1 foot contours of course, but it also shows old railroad beds, road beds, foundations, plus the creeks and river beds are shaded accurately for navigation through the adjacent trees.