  The Southern Galactic Plane Survey (SGPS) is an HI and 1.4-GHz continuum
survey of the 4th quadrant of the Galaxy at arcmin resolution. We present here
results on linearly polarized continuum emission from an initial
28-square-degree Test Region for the SGPS, consisting of 190 mosaiced pointings
of the Australia Telescope Compact Array, and covering the range 325.5 < l <
332.5, -0.5 < b < +3.5. Complicated extended structure is seen in linear
polarization throughout the Test Region, almost all of which has no correlation
with total intensity. We interpret the brightest regions of polarized emission
as representing intrinsic structure in extended polarization, most likely
originating in the Crux spiral arm at a distance of 3.5 kpc; fainter polarized
structure is imposed by Faraday rotation in foreground material. Two large
areas in the field are devoid of polarization. We argue that these voids are
produced by foreground HII regions in which the magnetic field is disordered on
scales of ~0.1-0.2 pc. We also identify a depolarized halo around the HII
region RCW 94, which we suggest results from the interaction of the HII region
with a surrounding molecular cloud.
