Erth refers to the collection of islands that make up the Empyrean and the islands beyond the Empyrean's direct control.  Erth is connected by the nightsea and divided into four quadrants by the powers Scions.

A word of interconnected glowing islands in a sea of darkness, the nightsea is the connective medium that allows travel between islands on Erth. Traveling the nightsea is not as easy as sailing on an ocean, and requires specially built slipships to traverse it.

The nightsea is ordered around the Core. The Core is formed from the Twelve Kingdoms, which are the center of the Scions power. Outside of the core is the Fringes, which is divided into four quadrants. The power of the Scions has yet to extend out to the Fringes, and the Military Police maintains a minimal presence there.

The Empyrean, also known as the Core and the Twelve Kingdoms, composes the center of the Erth. The Empyrean is ruled over by the Twelve Rulers, who are from families directly chosen by the Scions. The islands of the Empyrean have less freedom than the Fringes, and are often ruled with an iron fist. 

The Fringes are islands outside of the direct control of the Scions and the Military Police. Each island has differing levels of technological development as well as governing styles, with some even being controlled by the lesser nobles from the Empyrean. On occasion, some islands from the Fringes are assimilated into the Empyrean, and new islands are formed out within the darkness of the nightsea.