  We have performed a statistical analysis of a sample of 1100 extra-galactic
rotation measures (RMs) obtained from the literature. Using a subsample of
approximately 800 reliable RMs we compute a rotation measure sky and determine
reliable large scale features for the line of sight Galactic magnetic field. We
find that the influence of the Milky Way can be seen up to roughly 30 degrees
on either side of the Galactic plane. Furthermore we observe an excess of RM on
spatial scales between 30 degrees and 50 degrees in the region of the Galactic
Plane. Additionally, the support for a bisymmetric spiral Galactic magnetic
field is significantly reduced in our analysis.
