The in situ magnetic field and plasma measurements from the International Cometary Explorer (ICE) Mission obtained on September 11, 1985 are compared with CCD images of P/Giacobini-Zinner (G-Z) acquired with the 3.6 m Canada-France-Hawaii Telescope (CFHT) on Mauna Kea, Hawaii and a slit spectrogram from Lick Observatory during the same period. The CFHT image at ~3.5 hr after the ICE encounter showed a short central ion tail with a diameter of ~3¿103 km and a length of ~2¿104 km as observed in the H2O+ bandpass centered at 7025 ¿. There was no distinct evidence of fine structure or ray activity. The Lick spectrogram of the H2O+ emissions taken ~0.5 hr post-encounter with the slit perpendicular to the sun-comet line showed an ion tail with a diameter of 1.2¿104 km. The ICE observations revealed a well defined 9.6¿103 km diameter magnetotail composed of two magnetic lobes in pressure equilibrium with a high beta central plasma sheet. These differing measures of tail width are found to be mutually consistent if the ion emissions observed at Earth originate in a slab-shaped plasma sheet whose orientation is controlled by the direction of the interplanetary magnetic field. The results of this study also suggest that some thinning and thickening of cometary type I tails, usually attributed to plasma instabilities, may be due to changes in the angle at which the plasma sheet is viewed as IMF direction varies.