  Motivated by recent efforts to encode 11D supergravity in 4D N=1 superfields,
we introduce a general covariant framework relevant for describing any higher
dimensional supergravity theory in external 4D N=1 superspace with n additional
internal coordinates. The superspace geometry admits both external and internal
diffeomorphisms and provides the superfields necessary to encode the components
of the higher dimensional vielbein, except for the purely internal sector, in a
universal way that depends only on the internal dimension n. In contrast, the
N=1 superfield content of the internal sector of the metric is expected to be
highly case dependent and involve covariant matter superfields, with additional
hidden higher dimensional Lorentz and supersymmetry transformations realized in
a non-linear manner.
