The unit comes with a base map.
But, it is not high definition (does not have 1 foot contour lines).
You could record on a calm day.
Then, using PC software, such as Humviewer, review the recordings at
your PC, and note the gps coordinates of any structure you find useful.
As you move the mouse, it will show you the depth and gps coordinates of
the location where the mouse is pointing.
Then, you could create Waypoints by keying those coordinates into your unit,
and giving them Waypoint names.
Or, you could use the PC software HumminbirdPC to add the Waypoints
to an SD card, which will automatically load into your unit's memory
when you put the SD card into one of the card slots.
Then, when you are on the water, whatever map you are using
(base, Navionics, Lakemaster). The Waypoints would be overlayed
onto your map.