Magnetic field structures are analyzed for both the ionospheric hole region and the magnetosheath-ionosphere interaction region of the nightside of Venus, in search of possible coupling between these two regimes. A magnetic coordinate system based on the directions of the solar wind and the interplanetary magnetic field (IMF) is found to order the data reasonably well, allowing consistent superposition of observational data from individual passes of the Pioneer Venus orbiter. The main findings are (1) ionospheric holes form in a zone of ¿45¿ magnetic latitude covering possibly the entire width of the Venus wake in the longitudinal direction; (2) the magnetic field within the holes is strong and ordered, and its direction is determined by the IMF direction, being consistent with the field line draping concept; (3) the magnetic field direction in the holes, particularly at low altitudes near the terminator, shows evidence for the existence of strong plasma flow toward the antisolar meridian in the direction parallel to the magnetic equatorial plane; and (4) the average magnetic field distribution in the nightside magnetosheath also evidences strong plasma flow toward the antisolar meridian. Together these results strongly indicate that the magnetosheath plasma flow in the wake region plays an important role in forming the ionospheric holes, through deformation of the nightside ionopause. These results are combined in a model of the three-dimensional magnetic field structure around the ionosphere of Venus.