a two dimensional shape can be simplified as a collection of points.
the points can then be complex number represented as well as a well chosen origin for convenient point rotations.
the shape is then effectively rotated.
the creation of a rotating shape using complex numbers is quite interesting as well as useful. for example in robotics in real-time navigation, the CORDIC FAQ can serve as a super quick means of rotating a spacial image.
a google search with keywords "complex number rotation" (no quotes) found the following diverse references
Using Quaternions to Represent Rotation By: Laura Downs
http://www.genesis3d.com/~kdtop/Quaternions-UsingToRepresentRotation.htm
quaternions are a kind of "3D" complex number and great to represent dynamic spacial operations such as cartesian coordinates for trajectory paths (think missile).