  A new, much improved model of the Galactic Magnetic Field (GMF) is presented.
We use the WMAP7 Galactic Synchrotron Emission map and more than forty thousand
extragalactic rotation measures to constrain the parameters of the GMF model,
which is substantially generalized compared to earlier work to now include an
out-of-plane component (as suggested by observations of external galaxies) and
striated-random fields (motivated by theoretical considerations). The new model
provides a greatly improved fit to observations. Consistent with our earlier
analyses, the best-fit model has a disk field and an extended halo field. Our
new analysis reveals the presence of a large, out-of-plane component of the
GMF; as a result, the polarized synchrotron emission of our Galaxy seen by an
edge-on observer is predicted to look intriguingly similar to what has been
observed in external edge-on galaxies. We find evidence that the cosmic ray
electron density is significantly larger than given by GALPROP, or else that
there is a widespread striated component to the GMF.
