Data sampling is also relevant to data fitting. The atomic coordinates are often transformed into variables to characterize the chemical environments of the system with appropriate symmetry properties. Indeed, the density and the representative of the sampling should be measured under the representation of the fitting, for instance, the PIP spanned space for PIP-NN, or the atom-centered symmetry function space for HD-NN. Data sampling is also relevant to the research target. Reaction dynamics reach much wider configurations than those only for ro-vibrational spectra simulations.