A dilation is a transformation that changes the size but not the shape of a pre-image. The image of a dilation is not congruent to the pre-image, therefore a dilation is not an isometry.  A dilation stretches or shrinks the original figure.  Since the pre-image and image are the same shape, they are similar figures.  Similarity is discussed in more detail a little later in this unit.

A dilation occurs when a scale factor,  or magnitude, is applied to a shape originating from a fixed point, called the center of dilation.  The figure below demonstrates a dilation resulting in a shrink and the center of dilation is point O.

dilation image