Data sets used to prepare Figures 1-6, 8-13 and S1-S4 in the Journal of Chemical Physics article entitled "Transition from a phosphate to niobate network structure in vitreous Nb2O5-NaPO3."  The data sets describe the structure of the model crystalline compounds NbOPO4 and NaNbO3 and the structure of glasses in the Nb2O5-NaPO3 pseudo-binary system as measured using neutron and high-energy x-ray diffraction. They also give the predictions of an analytical model for the glass structure and a comparison of these predictions with the results obtained from nuclear magnetic resonance (NMR) spectroscopy and x-ray photoelectron spectroscopy (XPS).