Yeah, I don't know what those two brown splotches are, either. Probably diet Coke.
This idea map turned out to be way more complex than I initially thought it would. The inner ring:
South Louisiana is a place of concurrent fictions: mutually acceptable fictions, metafictions, and alternative realities. "Where" you are in south Louisiana is a matter of place and perception. Here we have the palimpsest in action, because at any given time, one could be traversing through a site that has been previously transcribed and set, but forgotten over time or through human intervention. The key here is that things are static in a palimpsest, not dynamic.
Carcosa is a metafictional place, taken from a work of fiction (though we are never clear on how exactly the cult learns of the existence of Carcosa, or how they characterize it to themselves beyond Miss Delores's ravings). It is both a place, in that it exists in the abandoned fort on the grounds of the Childress place, and an idea, in that it seems to be a person to be worshiped, at least according to Miss Delores. It is a place out of time, asynchronous with the outside world, as Childress has constructed it in the abandoned fort.
The relationship between place and reality grows less certain the farther the True Detective narrative progresses. How real is a place? Where is it found? When a cult's members name a place Carcosa, then conduct a series of assaults and murders over the course of years without being caught, how real is any place not of Carcosa? Is Carcosa ultimately the real place, and is the area of south Louisiana around it the "real" fiction? And if the two places coexist, do they do so through multiple synchronous timelines? A palimpsest becomes problematic when trying to accommodate both Carcosa and south Louisiana once the murders begin, because it is so frequently overwritten.
Because of the power structures in south Louisiana--political power linked with money and pedigree--things can be hidden in plain sight. Errol Childress can kidnap, torture, and murder children and teenagers so long as he chooses the poor and powerless, because no one is likely to notice that they are anything more than suspected runaways. Other members of the cult can continue their practices alongside Childress so long as they adhere to similar social codes, drawing their members from one caste/class and their victims from another. The personal code of the cult members is in the words, phrases, and images they use in their practices, making up what is essentially the cant of the initiate. The code is occult, both in the sense that it is hidden and that it is cult-like. The codes become signs of both recognition and occlusion.
Yet there are also the codes that Cohle and Hart live by, both personally and professionally. Both men have a personal code, and they have made sacrifices that are elemental to their respective codes. Cohle sacrifices his personal life even as he clings to his work as an investigator, while Hart's multiple codes destroy his personal life without affecting his professional one. Both men have a professional code as police investigators, which makes them effective in their work, Cohle especially. Their ability to catch criminals depends on their ability to understand the codes criminals live by and predict the criminals' behavior. In other words, their suspicions about the codes of others are derived from their own codes.