Introduction to Matrices - 3D Math Primer for Graphics and Game Development - page 128

Figure 4.3. Drawing an object inside the box helps visualize the transformation
This parallelogram is also known as a “skew box.” Drawing an object
inside the box can also help, as illustrated in Figure 4.3.
Now it is clear that our example matrix M not only rotates the coordi-
nate space, it also scales it.
We can extend the techniques we used to visualize 2D transformations
into 3D. In 2D, we had two basis vectors that formed an L—in 3D, we have
three basis vectors, and they form a “tripod.” First, let's show an object
before transformation. Figure 4.4 shows a teapot, a unit cube, and the
basis vectors in the “identity” position.
Figure 4.4
Teapot, unit cube, and basis vectors before
transformation
(To avoid cluttering up the diagram, we have not labeled the +z basis
vector [0,0,1], which is partially obscured by the teapot and cube.)