  Fronts are regions of transition from one state to another in a medium. They
are present in many areas of science and applied mathematics, and modelling
them and their evolution is often an effective way of treating the underlying
phenomena responsible for them. In this paper, we propose a new approach to
modelling front propagation, which characterises the evolution of structures
surrounding radiative sources. This approach is generic and has a wide range of
applications, particularly when dealing with the propagation of phase or state
transitions in media surrounding radiation emitting objects. As an
illustration, we show an application in modelling the propagation of ionisation
fronts around early stars during the cosmological Epoch of Reionisation (EoR)
and show that the results are consistent with those of existing equations but
provide much richer sources of information.
