Graphene and hexagonal boron nitride (h-BN) nanoribbons of diverse widths and edge geometries are laterally repeated to form commensurate, single-layer, hybrid honeycomb structures. The resulting composite materials appear as continuous, one atom thick stripes of graphene and BN having the average mechanical properties of constituent structures. However, depending on the widths of constituent stripes they can be metal or semiconductor with band gaps in the energy range of the visible light. These two-dimensional (2D) composite materials allow strong dimensionality in electrical conductivity and undergo transition from 2D to one-dimensional (1D) metal in a 2D medium, resulting in multichannel narrow conductors. As for the composite ribbons, such as one dielectric BN stripe placed between two graphene stripes with bare zigzag edges, charge separation of opposite polarity is possible under applied electric field and they exhibit resonant tunneling effects at nanoscale. Graphene/BN composite materials also form stable single-wall nanotubes with zigzag or armchair geometries.