From the bulge to the outer disc: StarHorse stellar parameters,
  distances, and extinctions for stars in APOGEE DR16 and other spectroscopic
  surveys
  We combine high-resolution spectroscopic data from APOGEE-2 Survey Data
Release 16 (DR16) with broad-band photometric data from several sources, as
well as parallaxes from {\it Gaia} Data Release 2 (DR2). Using the Bayesian
isochrone-fitting code {\tt StarHorse}, we derive distances, extinctions and
astrophysical parameters for around 388,815 APOGEE stars, achieving typical
distance uncertainties of $\sim 6\%$ for APOGEE giants, $\sim 2\%$ for APOGEE
dwarfs, as well as extinction uncertainties of $\sim 0.07$ mag when all
photometric information is available, and $\sim 0.17$ mag if optical photometry
is missing. {\tt StarHorse} uncertainties vary with the input spectroscopic
catalogue, with the available photometry, and with the parallax uncertainties.
To illustrate the impact of our results, we show that, thanks to {\it Gaia} DR2
and the now larger sky coverage of APOGEE-2 (including APOGEE-South), we obtain
an extended map of the Galactic plane, providing unprecedented coverage of the
disk close to the Galactic mid-plane ($|Z_{Gal}|<1$ kpc) from the Galactic
Centre out to $R_{\rm Gal}\sim 20$ kpc. The improvements in statistics as well
as distance and extinction uncertainties unveil the presence of the bar in
stellar density, as well as the striking chemical duality in the innermost
regions of the disk, now clearly extending to the inner bulge. We complement
this paper with distances and extinctions for stars in other public released
spectroscopic surveys: 324,999 in GALAH DR2, 4,928,715 in LAMOST DR5, 408,894
in RAVE DR6, and 6,095 in GES DR3
