Definition
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.