  We use the Ward identities corresponding to general linear transformations,
and derive relations between transport coefficients of $(2+1)$-dimensional
systems. Our analysis includes relativistic and Galilean invariant systems, as
well as systems without boost invariance such as Lifshitz theories. We consider
translation invariant, as well as broken translation invariant cases, and
include an external magnetic field. Our results agree with effective theory
relations of incompressible Hall fluid, and with holographic calculations in a
magnetically charged black hole background.
