Quote Originally Posted by Larkas View Post
Now these are things that I never quite wrapped my head around:

1) Both Planescape (IIRC) and 3.5 describe the Elemental Planes as both infinite and bordering other Elemental (or Para-Elemental, or Quasi-Elemental, or Energy) Planes. Hence, where the Water Elemental Plane borders the Air Elemental Planes, you'd have steam. But how can something be both infinite AND border something else?
Well, I'll explain by analogy.

Start at 0, and count upward by ones. The set of numbers you count (if you could count forever) would be "infinite;" that is to say, it is uncountable and unending. Nonetheless, no matter how high you count, I always have one "end" - the zero cannot move. Now start at zero and count downward by ones. Again, you have an "infinite" set of numbers - you will never reach a number so low that it cannot be bested by subtracting one - yet it has a defined limit.

Compare both of these to the entire set of integers - it is also infinite, and yet logically must be larger than either set individually, comprising as it does both of the previous infinities. Now take the real numbers - infinitely more infinite than the integers.

The way of the planes is such that there's no physical (0,0) at which all four elemental planes would originate and move away from, nor is there a point (X, 0) or (0, Y) that is "fixed" in planar space where the border is located. Rather, these realms are infinite, and within these realms exists a border with another, which can be traveled to but is not a defined PHYSICAL limit.

2) The same applies for the Outer Planes in some measure. There are gates, so it's not exactly a border. But there are also River Styx and Oceanus, the Yggdrasil and other things that link stuff. How can you picture, for example, Oceanus passing through Arcadia and Ysgard? Do the shores form a continuum (and, thus, there is a real border, like in the Inner Planes), or does only a tiny fraction of the river exist in both planes (imagine: patch of land-river-patch of land)? Both are somewhat strange propositions!
Again a metaphysical quirk - the shores do not (typically) form a continuum, nor do the rivers, the tree and the mountain have defined points at which there is a changeover. The analogy for this would be to go into Paint and draw a series of lines one next to another that shift from (255,0,0) to (255,255,0). Looking at such a band of color, you could tell me that you started at red and went to yellow, and you could probably point out orange to me, but is where you think orange begins the same place that I think orange begins? Do you think you would pick the same place at a glance, every time? And when you have determined where orange begins, will you be able to say, conclusively, looking one pixel to the left, that the line to the left is definitively "red" and not "orange?"

3) In Planescape, I remember some locations changing planes because of a shift in alignment. A place in Mechanus that became too Good-aligned could suddenly become part of Elysium. Now, how do that work? Is there a land transfer, or are only buildings and/or features transfered?
There can be a land transfer from time to time, too, though the land would gradually take on traits in accordance with its new environment. A transition from Mechanus to Elysium is almost certainly out of the question, however - goodness appearing in pure law would move a location into Arcadia first, then Celestia, then Bytopia. It's not the most sudden of transitions. There won't be a crater left over or a town crushed under SURPRISE TOURISM ROCK, though.