Acknowledgements. We thank  Rosanna Sordo  for comments on a preliminary version of this paper. This work has used the following software products: IDL (https://www. l3harrisgeospatial. com/Software-Technology/ IDL), HEALPix (https://healpix. sourceforge. io/),Matplotlib (Hunter 2007, https://matplotlib. org),SciPy (Virtanen et al. 2020, https: //www. scipy. org),and  NumPy  (Harris et al. 2020, https://numpy. org). This research has made use of the SIMBAD database, operated at  CDS, Strasbourg, France. The full acknowledgements are available in Appendix A. Research for European Astronomy Training (GREAT-ITN) network; -the  European Cooperation in Science and Technology (COST)  through  COST Action   CA18104  ' Revealing the Milky Way with Gaia (MW-Gaia )'; -the  European Research Council (ERC)  through grants  320360 ,  647208 , and  834148  and through the  European Union 's  Horizon 2020 research and innovation and excellent science programmes  through  Marie Skłodowska-Curie  grant  745617  ( Our Galaxy  at full HD -Gal-HD) and 895174 (The build-up and fate of self-gravitating systems in the Universe) as well as grants  687378  ( Small Bodies :  Near and Far) ,  682115  ( Using the Magellanic Clouds to Understand the Interaction of Galaxies ), 695099 (A sub-percent distance scale from binaries and  Cepheids -CepBin) ,  716155  ( Structured ACCREtion Disks -SACCRED), 951549 (Subpercent calibration of the extragalactic distance scale in the era of big surveys -UniverScale ), and  101004214  ( Innovative Scientific Data Exploration and Exploitation Applications for Space Sciences -EXPLORE ); -the  European Science Foundation (ESF) , in the framework of the  Gaia Research for European Astronomy Training Research Network Programme (GREAT-ESF ); -the  European Space Agency (ESA)  in the framework of the  Gaia  project, through the  Plan for European Cooperating States (PECS)  programme through contracts  C98090  and  4000106398/12/NL/KML  for Hungary, through contract  4000115263/15/NL/IB  for Germany, and through  PROgramme de Développement d'Expériences scientifiques (PRODEX)  grant  4000127986  for Slovenia; -the  Academy of Finland  through grants  299543 ,  307157 ,  325805 ,  328654 ,  336546 , and  345115  and the  Magnus Ehrnrooth Foundation ; -the  French Centre National d'Études Spatiales (CNES) , the  Agence Nationale de la Recherche (ANR)  through grant  ANR-10-IDEX-0001-02  for the ' Investissements d'avenir' programme , through grant  ANR-15-CE31-0007  for project ' Modelling the Milky Way in the Gaia era ' (MOD4Gaia), through grant  ANR-14-CE33-0014-01  for project 'The  Milky Way disc formation in the Gaia era ' (ARCHEOGAL), through grant  ANR-15-CE31-0012-01  for project ' Unlocking the potential of Cepheids as primary distance calibrators' (UnlockCepheids ), through grant  ANR-19-CE31-0017  for project ' Secular evolution of galxies ' (SEGAL), and through grant  ANR-18-CE31-0006  for project ' Galactic Dark Matter' (GaDaMa ), the  Centre National de la Recherche Scientifique (CNRS)  and its  SNO Gaia of the Institut des Sciences de l'Univers (INSU) , its  Programmes Nationaux: Cosmologie et Galaxies (PNCG) ,  Gravitation Références Astronomie Métrologie (PNGRAM) ,  Planétologie (PNP) ,  Physique et Chimie du Milieu Interstellaire (PCMI) , and  Physique Stellaire (PNPS) , the ' Action Fédératrice Gaia' of the Observatoire de Paris , the  Région de Franche-Comté , the  Institut National Polytechnique (INP)  and the  Institut National de Physique nucléaire et de Physique des Particules  ( IN2P3 ) co-funded by  CNES ; -the  German Aerospace Agency (Deutsches Zentrum für Luft-und Raumfahrt e.