The Geographical Society of Avernus (the main branch, anyway) is located in Janus.
It's purpose: Basically the gathering of information of geographical, anthropological, social and political information, and the maintenance of an archive for all the information gathered.
It's members: Highly qualified "intellectuals" (well, somewhat), anybody who can prove his neutrality in the big conflicts that shake Avernus and who has no other binding obligation. Oh, yeah, and who passes some sort of exam to prove that he/she/it actually would be an asset to the GSA.
It's financing: Geographers are much sought after consultants. Many trading companies employ licensed Geographers when establishing trading posts, and can hire them from the GSA at a rate reflecting the danter and the complexity of the task - always providing that the GSA always has access to whatever the geographers discover, no matter who pays them.
It's policy: Well. There are always rumors that they aspire to become a political powerhouse with all of the information they have about all of Avernus (and supposedly beyond), but officially they are just interested in the accumulation of information and basically act as just another Combine.
It's headquarters: A well-guarded complex - there are always people who would love to get at their information and their (considerably valuable) equipment. They also have a large collection of ancient artifacts collected on their more archaeological missions.
It's structure: At the head, there is the board of directors, each controlling one of the subsections (archaeology, salvage, morphology, climateology, linguistics, etc.). These subsections vary from term to term, and they are created or disbanded by the general assembly of geographers. The board controls the administration and the budget. They are advised by a small and well-maintained Overmind - which is not widely known outside of the GSA, since, after all, the Shogunate (for example) makes a wonderful employer.