  We investigate the distribution and properties of Faraday rotating and
synchrotron emitting regions in the Galactic ISM in the direction of the
Galactic anti-centre. We apply Faraday tomography to a radio polarization
dataset that we obtained with the WSRT. We developed a new method to calculate
a linear fit to periodic data, which we use to determine rotation measures from
our polarization angle data. From simulations of a Faraday screen + noise we
could determine how compatible the data are with Faraday screens. An
unexpectedly large fraction of 14% of the lines-of-sight in our dataset show an
unresolved main component in the Faraday depth spectrum. For lines-of-sight
with a single unresolved component we demonstrate that a Faraday screen in
front of a synchrotron emitting region that contains a turbulent magnetic field
component can explain the data.
