Lowrance 520C question

[jlingle]

On the features of this fishfinder, it lists that it has maps of over 3000 lakes in the unites states. Are these maps build into the software of the unit, or do you have to purchase the cards to be able tosee these? I know you can buy data cards like the Navionics and such for these fishfinders, but if they come pre-loaded with some maps already on the unit..... then what would be the difference?

This might be a stupid question, but if anybody knows, I'd sure appreciate it if you'd enlighten me.

[tspergin]

you have the maps already in the unit but the navonics and other card maps are more detailed and show depth contours and wrecks and points of interest such as marinas and docks and others