Affinity also termed affinites or affine transformations, as defined by Coxeter and Greitzer (1967), in terms of transformations, preserves collinearity and thus takes parallel lines into parallel lines. The most common type of affinity is similarity. Another type is the procrustean stretch. As defined by March and Steadman (1974), in terms of mapping, affinity has the following invariant properties: parallelism, cross-ratio and neighbourliness.