Icejohn,
I have the Garmin 70dv unit, the base mapping is really great for Oneida for example, 1ft contours, all buoy locations, etc.
Way better than the base Lowrance, or hummingbird base.
It is highly tunable with settings, way more so than my ability anyhow.
The only complaint I have is it is not NEMA 2000, that would have been nice for the engine telemetry display.
-Perch