We consider models for the plateau transition in the integer quantum Hall
effect. Starting from the network model, we construct a mapping to the Dirac
Hamiltonian in two dimensions. In the general case, the Dirac Hamiltonian has
randomness in the mass, the scalar potential, and the vector potential.
Separately, we show that the network model can also be associated with a
nearest neighbour, tight-binding Hamiltonian.Comment: Revtex, 15 pages, 7 figures; submitted to Phys. Rev.