All-sky view of the angle of polarization at 30 GHz, rotated by 90° to indicate the direction of the Galactic magnetic field projected on the plane of the sky. The colours represent intensity, dominated at this frequency by synchrotron emission. The “drapery” pattern was obtained by applying the line integral convolution (LIC; Cabral & Leedom 1993) procedure using an IDL implementation provided by Diego Falceta-Gonçalves (http://each.uspnet.usp.br/fgoncalves/pros/lic.pro). This gives an effective way of visualizing regions where the field is coherent, but where the field varies significantly along the line of sight, the orientation pattern is irregular and difficult to interpret.