What map does Gamin unit use?

What map card or map does Garmin unit use/take? Also can you view their map online like how you can view Navionics maps online?

Garmin units use Garmin mapping

http://lakes.garmin.com

thanks! Im looking at that website and can't see the contour lines on the lakes, does Garmin not allow you to see that on the website?

Not that I know of. I've only looked at my home lake. But the legend on the left gives the detail. For example, Fontana Lake, NC 1 ft contours.