  We study the ratio $R\equiv\mu G_E(Q^2)/G_M(Q^2)$ of the proton at very small
values of $Q^2$. Radii commonly associated with these form factors are not
moments of charge or magnetization densities. We show that the form factor
$F_2$ is correctly interpretable as the two-dimensional Fourier transformation
of a magnetization density. A relationship between the measurable ratio and
moments of true charge and magnetization densities is derived. We find that
existing measurements show that the magnetization density extends further than
the charge density, in contrast with expectations based on the measured
reduction of $R$ as $Q^2$ increases.
