It is customary to define the time-frequency plane such that time and
frequency are mutually orthogonal coordinates. Representations of a si
gnal in these domains are related by the Fourier transform. We conside
r a continuum of ''fractional'' domains making arbitrary angles with t
he time and frequency domains. Representations in these domains are re
lated by the fractional Fourier transform. We derive transformation, c
ommutation, and uncertainty relations among coordinate multiplication,
differentiation, translation, and phase shift operators between domai
ns making arbitrary angles with each other. These results have a simpl
e geometric interpretation in time-frequency space.