The Cartesian plane is in ℝ^2. Any point can be expressed as a combination of (x,y) where both x,y ∈ ℝ. That means that both x and y are members of the set of

The Cartesian plane is in ℝ^2. Any point can be expressed as a combination of (x,y) where both x,y ∈ ℝ. That means that both x and y are members of the set of real numbers. A 3D graph is in ℝ^3. Any point can be expressed as (x,y,z), where x,y,z ∈ ℝ. A 4D graph is in ℝ^4. Any point can be expressed as a combination of (x,y,z,w), where x,y,z,w ∈ ℝ. Unfortunately, human vision is limited to three dimensions, so only four different perspectives are available (4 choose 3): (x,y,z), (x,y,w), (y,z,w), and (x,z,w). Moreover, the 3D must be collapsed into a 2D for presentation on the screen.