[whiterknight]

Affine transforms for N dimensions can be represented as matrices/linear maps in dimension N+1

[eigenket]

Sure, but that isn't what they're doing on that webpage. They're just directly applying linear maps to shapes in R^2.

You can represent a wild variety of things by linear maps on suitably enlarged spaces.

[whiterknight]

Agreed. Context: This sub thread is discussing how to interpret matrices as an abstract thing that does something as opposed to the mechanics of multiplying