Yora
Legend
Strictly speaking, a setting always only needs what the PCs interact with.
But interaction is not just what the PCs are acting on, but also what is acting on the PCs. Interactions are constantly happening far beyond the PCs' line of sight. If the players run into and talk with traveling merchants from a distant land, the scene is affected by that distant land. Even if it has no map and the single named city is the one the merchants come from, this interaction with the merchants can be significantly affected by the vague image the GM has of the land.
There does not have to be a lot of detail for anything that exists beyond the boundaries of the current campaign, but if you want to avoid having the campaign feel like taking place in a sealed bubble, there needs to be something that is touching the boundaries.
But interaction is not just what the PCs are acting on, but also what is acting on the PCs. Interactions are constantly happening far beyond the PCs' line of sight. If the players run into and talk with traveling merchants from a distant land, the scene is affected by that distant land. Even if it has no map and the single named city is the one the merchants come from, this interaction with the merchants can be significantly affected by the vague image the GM has of the land.
There does not have to be a lot of detail for anything that exists beyond the boundaries of the current campaign, but if you want to avoid having the campaign feel like taking place in a sealed bubble, there needs to be something that is touching the boundaries.