Complex sentence: The islands, covering a combined area of slightly over, are of volcanic origin and while three of them (Sal, Boa Vista and Maio) are fairly flat, sandy and dry, the remaining ones are generally rockier and have more vegetation.
Split into simpler sentences: The islands, covering a combined area of slightly over, are of volcanic origin. While three of them (Sal, Boa Vista and Maio) are fairly flat, sandy and dry, the remaining ones are generally rockier and have more vegetation.