Different film deposition techniques have been found to generate distinct grain morphologies and defect distributions, which can result in a wide distribution of local field intensities. We have developed a lattice element model of an inhomogeneous medium, which we use to self-consistently determine the local internal electric field and polarization. We use this method to show the sensitivity of the polarization to defect shape. The results of this method predict the local field to have a large range of values within the film and have been used to identify regions where the local field is a maximum.