In this paper we consider charge density waves in defective lattice structures. Just as in nondefective lattices, we find that the Fermi surface plays an important role in supercell dimensions. In particular, a correspondence is found between the Fermi surfaces of the defective and the nondefective lattices. The concept of an effective band filling is introduced, which may be understood as the band filling for which the fully occupied lattice mimics the Fermi surface of the partially occupied lattice. To demonstrate the efficacy of this method, the superstructures of La10Se19, Cs3Te22, RbDy3Se8, and Dy65.33Se120 are studied. Fermi surfaces from both Huckel and extended Huckel tight-binding theories allow the rationalization of the defect lattice structures found in these systems. Finally a simple model based only on nearest neighbor interaction is found to preserve most of the essential features of the Huckel and extended Huckel treatments.