  We present an analytical scaling theory for localization in a two-dimensional
hierarchical network model that is designed to represent phase-coherent
electron transport in the quantum-Hall regime. Scaling expressions for both the
longitudinal and Hall resistivities are derived. In agreement with recent
numerical studies, we find that the Hall resistivity is quantized in the
metallic phase but diverges in the insulating phase. This suggests that the
characteristics of a quantized Hall insulator can occur only in the presence of
a strong dephasing mechanism.
