In mathematics, a dilation is a function f {\displaystyle f} from a metric space M {\displaystyle M} into itself that satisfies the identity d = r d {\displaystyle d=rd} for all points x, y ∈ M {\displaystyle x,y\in M}, where d {\displaystyle d} is the distance from x {\displaystyle x} to y {\displaystyle y} and r {\displaystyle r} is some positive real number. Wikipedia