  We clarify the physical origin and meaning of the two-dimensional
relativistic densities of the light front formalism. The densities are shown to
originate entirely from the use of light front time instead of instant form
time, which physically corresponds to using an alternative synchronization
convention. This is shown by using tilted light front coordinates, which
consist of light front time and ordinary spatial coordinates, and which are
also used to show that the obtained densities describe a system at rest rather
than at infinite momentum. These coordinates allow all four components of the
electromagnetic current density to be given clear physical meanings. We
explicate the formalism for spin-half targets, obtaining charge and current
densities of the proton and neutron using empirical form factor
parametrizations, as well as up and down quark densities and currents. Angular
modulations in the densities of transversely-polarized states are explained as
originating from redshifts and blueshifts due to quarks moving in different
longitudinal directions.
