  We consider magnetotransport in high-mobility 2D electron gas in a
non-quantizing magnetic field. We employ a weakly chiral network model to test
numerically the prediction of the scaling theory that the transition from an
Anderson to a quantum Hall insulator takes place when the Drude value of the
non-diagonal conductivity is equal to 1/2. The weaker is the magnetic field the
harder it is to locate a delocalization transition using quantum simulations.
The main idea of the present study is that the position of the transition does
not change when a strong local inhomogeneity is introduced. Since the strong
inhomogeneity suppresses interference, transport reduces to classical
percolation. We show that the corresponding percolation problem is bond
percolation over two sublattices coupled to each other by random bonds.
Simulation of this percolation allows to access the domain of very weak
magnetic fields. Simulation results confirm the criterion \sigma_{xy}=1/2 for
values \sigma_{xx}\sim 10, where they agree with earlier quantum simulation
results. However for larger \sigma_{xx} we find that the transition boundary is
described by \sigma_{xy} \sigma_{xx}^k with k= 0.5, i.e., the transition takes
place at higher magnetic fields. The strong inhomogeneity limit of
magnetotransport in the presence of a random magnetic field, pertinent to
composite fermions, corresponds to a different percolation problem. In this
limit we find for the delocalization transition boundary \sigma_{xy}
\sigma_{xx}^{0.6}.
