  Interstellar magnetic fields play critical roles in many astrophysical
processes. Yet despite their importance, our knowledge about magnetic fields in
our Galaxy remains limited. For the field within the Milky Way, much of what we
do know comes from observations of polarisation and Faraday rotation measures
(RMs) of extragalactic sources and pulsars. A high angular density of RM
measurements in several critical areas of the Galaxy is needed to clarify the
Galactic magnetic field structure. Using observations made with the VLA, we
have determined RMs for sources in regions of the Galactic plane not covered by
the Canadian Galactic Plane Survey (CGPS) and Southern Galactic Plane Survey
(SGPS). We have combined these new RMs with those determined from the CGPS and
SGPS and have produced a new model for the magnetic field of the Galactic disk.
