In my experience the best way to learn how to draw convincing fantasy maps is to:

1. observe how things work in real life and the rules that apply.

2. Apply those rules to your fantasy maps seeing which rules you can break without the map losing its ability to convince.

3. Play with the software and experiment with it.

There is a free pdf which gives you some 'rules' to creating convincing worlds - 'A Magical Society: Guide to Mapping' you can download on mapping fantasy worlds (it is really worth a read). WWW.EXP.CITYMAX.COM.

I don't use CC3 (yet!) but if it works anything like CC2, then I guess you made the ice-field by filling a poly with the ice field fill. Presumably you could draw further polys on the island/continents at the same lattitude with the same fill?

Anyway, hope this helps,

Ravs