  In the standard picture of radio pulsars, the radio emission arises from a
set of open magnetic field lines, the extent of which is primarily determined
by the pulsar's spin period, P, and the emission height. We have used a
database of parameters from 600 pulsars to show that the observed profile
width, W, follows W proportional to P^-0.3 albeit with a large scatter,
emission occurs from heights below 400 km and that the beam is underfilled.
Furthermore, the prevalence in the data for long period pulsars to have
relatively wide profiles can only be explained if the angle between the
magnetic and rotation axis decays with time.
