Models contain a summary of our present knowledge about the stars in the Milky Way. This knowledge is obviously imperfect and one expects many of the discrepancies between model simulations and real Gaia data to be due to the models themselves. However, at the level of our current knowledge, if a model performs sufficiently good accuracy compared to existing data, it can be used for Gaia validation (at the level of this accuracy). This is what we are doing in this set of tests. These tests supersede the validation with existing data in regions of the sky where data are too scarce, or in magnitude range where existing data are not accurate enough or incomplete, or in case they do not exist in large portions of sky (parallaxes).
Tests have been run in parallel on Gaia DR2 data and on GOG18 simulations (Luri et al.2014). Then distributions on the sky have been plotted for visual checking and values of mean and standard deviations have been inter-compared as a function of HEALPix, of latitudes and/or magnitudes. For the time being, tests on colours are not provided.