Circus is one of the Strange Stars' great wonders. No one knows who built the megastructure (it may even predate the Archaic Oikumene and be pre-human), but whoever it was had mastered technology beyond the reach of current civilization. It's gigantic ring has a radius of 1.9 million km and a width of about 1000 km, giving it a habitable surface area roughly 20 times that of Old Earth. It's rotational period is 24 hrs and it's tilted so that it's inhabitants experience roughly earth-like night and day. It's open to space, but centrifugal force and an upper "mesh" of radiation filtering nano hold a breathable atmosphere in.
In a system bordered by the Zuran Expanse, the Alliance, and the Instrumentality sphere, Circus has long been a center of trade. Its ruins attest to several stages of colonization by the human phyle. Modern, non-wilderness or waste sections of the great ring are a crazy quilt of petty kingdoms, communes, and experimental societies. These are the "zones"--or at least partial zones. The minimum size required of a political body for the term to be used is the subject of controversy.
The most famous area of Circus is actually a free city--actually a megapolis or ecumenopolis--without a single name. It's most often called Interzone, though it's vast spaceport-adjacent tourist area is known as the Strip. Interzone's boundaries are vague, but including all of it's favelas and industrial parks, it covers an an area only a little less than the surface area of Sol IV (Mars).
Spacers say there is no law in Interzone, but this is not strictly true. Rather it's a demarchy with minimalist government. The Wise Minds (a group of ancient infosophonts) select via lottery the anonymous rulers of the city--the Tsadikim--from among the populous. A Tsadik may serve for a few days or for a lifetime, based on the real-time evaluation of the Wise Minds. Every Tsadik (with the advice of the Minds) can create new laws at whim, though these must be approved by a majority of the other Tsadikim. Likewise, any Tsadik can supercede the decree of another with the same procedure. Tsadik can settle disputes among the populace themselves or a trial with a judge (this decision too is subject to review by the others).
The only immutable laws of Interzone are "property and self are sacred", "self-defense and common defense are a justification for violence", and "a contract is a contract."