Nonagons

Most Scarterrans have a favorite and/or least favorite deity but they tend to worship all nine of the Nine, at least a little bit.
Many locations array their temples or shrines to the Nine in a single place, outlined in a nonagon with a small field in between them. Thus if a Scarterran uses "the Nonagon" as a land mark they are probably referring to the nearest said cluster.
Most Nonagons are in rural areas and composed of nine fairly humble shrines. In larger settlements, each point of the Nonagon is a full temple and the plaza between the nine temples is usually quite large, often called the Temple Plaza or the Nonagon Plaza.
Not every large population center has a Nonagon. Not all local rulers accept all nine deities into their midst. Not all priesthoods are content to have their central temples so close to those of their rivals.
Many Nonagons in high population areas are incomplete with one, two, or three empty or missing representing groups that preferred to locate their temples elsewhere. Others maintain a figurehead public temple in the Nonagon and have their "real" temples elsewhere.

"Nonagon" in the common vernacular

Frequently, in casual conversation "the Nonagon" doesn't refer to a place, but it's a slang term for "all the local priesthoods" or "all the politically active priesthoods."
This is similar to how "the nobility" often refers to all highborn land holders in the area rather than to specific individuals.

Primary Related Location

Scarterra