I think it exists in your mind but it is a product of a process involving your thoughts, your notes, etc. I am not advocating for a platonic form of the setting or something (though I am sure there are GMs who take this view somewhere). It is a concept. A model. I am not saying it is real. I am saying it resides somewhere in between the two extremes being offered (total non existence, and real). It exists in that it has some objective parameters the GM can track and build on in his mind. When I am running a setting, I am regularly modeling it in my head. I am not saying that is a perfect model. When I likened it to a computer simulation, I made a point of calling it primitive because I am using very remedial instruments (notes, maps, sketches, outlines of institutions, outlines of political structures, descriptions, knowledge of what is happening in the setting, knowledge of what the PCs are doing). It isn't as perfect as a computer model by any stretch. but it s also clearly not the same as a method where there is no attention paid to the setting as a living world model. This isn't something where you always have this mental projection going on in your mind obviously. It stops and starts. But I can imagine it pretty clearly when I think about it (and again not everything: I am not saying I have a zoom in and zoom out objective map of the setting in my head---I am saying I have a workable model).
And also there can be more worked on and less worked on areas in the setting. Just out of necessity you may decide there is a vast basin to the west, but because you know it isn't likely to come up you don't tend to those details as much as the eastern provinces or something (though eventually you may need to: and there at least ought to be some idea of what is going on in that basin so the eastern provinces aren't in a vacuum).
I'm curious how your mental model would process the below to come to a result (rather than consulting a game's procedure for building a dice pool > rolling dice > interpreting result based on the action resolution mechanics). And I'm assuming you wouldn't "go to the dice" here? This would just be full GM extrapolation. Consider the following parameters and let me know what your instinct tells you would happen by answering the below questions (in like a sentence):
* Supernatural apocalypse so when people die their spirits don't crossover. They haunt the world. The sun "died", cities are tiny "points of light", little enclaves, each having to develop their own means for dealing with the horrific circumstances of the apocalypses. The land in between is called "The Deathlands" (you can imagine why).
* However, the powers-that-be in the city of Duskvol have engineered a functional but imperfect solution; infrastructure + a small group of personnel capable of preventing their city from being completely overwhelmed by spirits:
Infrastructure - Arcane Spirit Bells at an attuned Bellweather Crematorium ring out when someone dies. This sound channels through the Ghost Field (the arcane fabric of the world) and can only be heard locally. Deathseeker Crows then release from the belfry and move inexorably toward the ward of the death(s) and circling when they draw nearer the corpse(s). Back at Bellweather, there are special electroplasmic crematoriums to dissolve the spirit.
Personnel - The Spec Ops who handle the missions are few, but they are capable and geared to help them do the work of locating corpse(s) and getting it back to the crematoriums. This is very time sensitive and a short loop (well within a day...maybe within a few hours).
* Charterhall (where the Bellweather Crematorium is located) is on the far side of the city (Eastern end). Barrowcleft, the city's breadbasket (any other food must be imported in via the Electro-Rail trains that span The Deathlands and connect the dispirate cities of The Imperium) where The Radiant Farms are located, is situated on the West Wall of the big city.
* A massive death toll erupts, and secretly, in multiple places in Barrowcleft in the middle of the night. The scale and circumstance of this kind of event would profoundly strain The Spirit Wardens in terms of personnel/capability and finding each body comes with an uncomfortable margin-of-error, despite the resources afforded to the group.
So what happens and how do you mentally model/extrapolate "what happens" based on the above parameters?
1) Is there a massive outbreak of malevolent spirits in Barrowcleft that then feeds back into more spirits (a supernatural pandemic) as new people are killed and the situation force-multiplies? Is it completely contained? Partially contained?
2) If it is only partially contained, is there food shortages (and when does it start)? If its a complete cluster-eff, when does hysteria, famine, and violence (creating another feedback loop) overtake the city?
3) Does the city's elite rulership try to contain the newspread of the problem to the public? Or do they get out in front of it and let everyone know the dynamics in play? How does the public respond?
4) Do warring factions temporarily truce under a cease-fire banner due to the bigger fish to fry? Or do several/all use this as an opportunity?
5) Does the elite rulership declare martial law on the whole city, just the affected ward, what? Refugee crisis?
6) What resources do they martial in order to address the problem (whatever magnitude you decide it is)? Do they enlist the public and invest them with temporary authority/capability in order to bulwark the Spirit Wardens ranks?
Procedurally, how do you answer those questions? All extrapolation? Some dice?
If some dice, when, and how is that informed/what does it look like?
Ultimately, what are your answers?