Potential space has been mentioned here as the virtual space in which a player avatar can feasibly exist. We shall explore this space and its properties; most importantly how it can shape the challenge a game presents to the player.
Active space, which we have established is the space a player avatar can interact with in any given moment, is highlighted above in red. In blue, the potential space; that is to say the space said avatar can inhabit, ever.
With Tetris, potential space is an ever-changing void; the shape and capacity of which is dictated by the layout of the previously-deposited pieces and, to a lesser extent, the shape of the player avatar currently in play; the current piece being controlled by the player.
As a game of Tetris continues, potential space diminishes. This is concurrent with the game becoming more intense and challenging; a very safe assumption that can be made from this is that the challenge factor (or difficulty) of games is directly tied to the potential space availed to the player. This is not a completely universal truth, but we shall explore this later.
For now, a more ‘static’ example of potential space:
In this approximated diagram using Super Meat Boy as an example, we can notice a few things about potential space. First of which is that although there is empty space outside the level layout, the player avatar will not occupy this space in normal play (other means to do so may exist, such as hacking, but these are not considered here) — and so this is not potential space.
Another thing to notice is the buzzsaws effectively removing potential space. This is not a property of the space in and of itself nor the buzzsaw obstacles, but of the game’s inherent ruleset; if Meat Boy touches them, he expires and play is terminated, effectively acting as a barrier to the space they occupy. This could differ if the game rules allowed damage and an invincible ‘grace period’ during which the player character could occupy the same space as these hazards, but this is not the case here. Potential space is the product of active space and the game’s internal logic and/or physics.
To use a theatrical analogy; if active space is the player’s voice then potential space is the stage, hall, and anywhere else the acoustics allow said voice to be heard.