A square, a two-dimensional shape, exists on a plane, witch is a two-dimensional space. similarly, a cube is a three dimensional and exists in a volume, a three dimensional space.
Since the separation of the dots shows the pairs, we can take that square and plane represents the depiction of the square in two-dimensional space. The analogy continues with cube - space, where the space is three-dimensional Euclidean space in order to represent the cube.
