The algebra of observables of planar electrons subject to a constant background magnetic field B is given by A(theta)(R-2) circle times A(theta)(R-2) (theta = -4/eB), the product of two mutually commuting Moyal algebras. It describes the free Hamiltonian and the guiding center coordinates. We argue that A(theta)(R-2) itself furnishes a representation space for the actions of these two Moyal algebras, and suggest physical arguments for this choice of the representation space. We give the proper setup to couple the matter fields based on A(theta)(R-2) to electromagnetic fields which are described by the Abelian commutative gauge group G(c)(U(1)), i.e. gauge fields based on A(0)(R-2). This enables us to give a manifestly gauge covariant formul...