My 15yr old son was given a Hummingbird 778c by a gentleman in our camp. This unit is GPS capable. I'm not sure what that means, other than we will need to pick up a compatible GPS antenna puck. My question is, what map is used when on the GPS screen?? There is no where to insert a map card so will he be limited to a base map or can this unit be hooked up to a PC and a Navionics or lakemaster downloaded?? Any help regarding the capabilities of this unit are appreciated.

The unit does not have and can not have mapping. If you add a GPS antenna it will be a Track Plotter and not a Chart Plotter.

Look at the accessories listing at the bottom left of the unit description here:

http://store.humminbird.com/products/410759/778c

Wayne,, thank you for the reply and clarifying. Can you tell me wheat a track plotter is? Does that mean that he can save tracks/routes and way points, just without the map feature??

A Track Plotter is basically a blank screen that shows your tracks, waypoints, and planned routes.

The GPS function is the same with a Track Plotter and a Chart Plotter, just a Chart plotter has a map background. GPS is not mapping and mapping is not GPS.

Got it. Much appreciated Wayne!!