If your cutoff extends all the way down to DC, this indicates you have a continuous metallic photonic crystal. If not, you have a dielectric lattice, a discontinuous metallic lattice, or both. The width of the band gap corresponds to the dielectric contrast, although other factors contribute to width of the band gap like symmetry and pattern within the unit cell. The position of the band gap corresponds to lattice spacing, although refractive index also scales this. The rule-of-thumb is that the band gap occurs at a wavelength which is equal to around twice the period of the lattice (see Bragg gratings). I hope I answered your question!