This is just the bare bones of the planet. There are literally thousands of small islands that are not shown at this scale.
The large circular areas are the result of massive meteor strikes dating back to Araj's attempt to destroy Enegala. This was after Enegala started making his own creations without Araj's consent. This was long before the planet was inhabited. The areas surrounding these sea-filled craters are now a source of valuable metals and are plagued by volcanism.