Mapping will show you features of the lake bottom not easily recognizable from above ...

And as treelike mentions = the LakeMaster mapping adds extra mapping features like Depth Highlight/Range ...which allows highlighting a certain depth contour (with an adjustable range each side of that chosen Depth Highlight) ...

This will "paint" a green sidewalk on the map (using those chosen criteria) to make contour following very easy by simply keeping the boat icon on the "green sidewalk" on the map ...

Rickie