The map would always be oriented in the direction the phone is pointing. Standard courses would be marked, including your deviation. Depth alarms (based on chart position). Time to destination. Compass. Hmmmm!
Shall we take this one to Nokia? ;-) You can't be me, I'm taken
The real thing often comes with real time depth mapping, because silt tends to move, so at the edges of a channel you can't be sure of the safe depth. It also varies with tidal phase and season.
See e.g. here.
Also, Nokia might not go for it because there are a lot more drivers than boat owners. ;)
