The centerpiece of the game design is the Settlement. Settlements are both a place - they are permanent collections of structures - and a social grouping of characters. Being a "member of a Settlement" means that you are a part of the Settlement's ownership and management. A character might be physically within the walls of a Settlement, and might even have storage there and be operating out of the Settlement, the character is not a "member of the Settlement" unless that character is actually a part of the social structure system.
A character is really a combination of the experiences of the character as reflected by trained skills and learned character abilities, and their Settlement. The structures in the character's Settlement reflect the abilities the character can use, and the skills they can train. If a character leaves a Settlement and joins another, they may find that some abilities they used to have access to are unavailable, and new abilities that they couldn't previously use become unlocked.
Settlements are enmeshed in a multi-dimensional system of alignment & reputation. Settlements have restrictions on the characters that can join them based on their alignments (Law to Chaos, Good to Evil). Orthogonal to the classic alignment axis is the Reputation vector which roughly corresponds to how constructive the character's past actions have been with regards to the whole game. Characters who engage in meaningless killing will slide their alignment towards chaos and evil, and their reputations will be very poor. These choices will affect the kinds of Settlements characters can join - and since Settlement structures affect the abilities characters can use, their Settlement options have a bearing on how those characters are played.
Settlements also have structures that support the in-game economy, like markets and crafting facilities. Settlements may have Taverns where characters can gather to heal more quickly and engage in roleplaying and camaraderie. Sometimes NPCs will appear in Settlements and ask for help - creating opportunities to earn treasure and learn more about the lore of Pathfinder Online.
In the long term, the game will be driven by the Settlements. There are only limited numbers of places Settlements can be built, so the struggle to control territory, to build and defend Settlements will be the primary source of conflict between characters. Of course, we'll constantly be adding new territory to the edge of the map, so there will always be a frontier where a new group, or a group that has suffered a catastrophic setback, can go to seek new opportunities.
Settlements will have hundreds of characters as members. They can organize themselves in many different ways from dictatorships to pure democracies. They can set certain policies and tax rates. They can decide how to allocate various economic resources, and assign roles and responsibilities to characters who will act as managers of those resources. Settlements will have relationships with other Settlements and with Companies, and will have the ability to establish certain laws within the territories they control.