  A compact and elegant description of the electromagnetic fields in media and
in vacuum is attained in the differential forms formalism. This description is
explicitly invariant under diffeomorphisms of the spacetime so it is suitable
for arbitrary curvilinear coordinates. Moreover, it is independent of the
geometry of the underline spacetime. The bulk electric charge and current
densities are represented by twisted non-singular differential 3-forms. The
charge and current densities with a support on the low dimensional submanifolds
(surfaces, strings and points) naturally require singular differential forms.
In this paper, we present a covariant metric-free description of the surface,
string and point densities. It is shown that a covariant description requires
Dirac's delta-forms instead of delta-functions. Covariant metric-free
conservation laws for the low-dimensional densities are derived.
