If you are looking at a map(on your screen), the depths shown
there are static, and based on how good your map is.
Some Navionics maps have 1 foot contour lines.
Also, set chart detail to 'All' and spot soundings to 'Visible'
under your chart menu so that you can see all that your map offers.
The depth shown on the bottom or left of your unit is the depth
underneath your transducer. It is in real time, and has nothing to
do with any map.