The Oikumene
The novels take place in the Oikumene, which is a loose confederation of the civilized planets of the galaxy. The Oikumene shares some conceptual features with the Gaean Reach, which is his name for the civilized worlds in many of his other science fiction novels, and in the fictional timeline of Vance's work may be a precursor to the Reach. Earth exists in both universes, for example, and currencies based on unskilled labor appear in both, but most of the fictional planets don't overlap.
Read more about this topic: Demon Princes, Setting