The completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey:
  Large-scale Structure Catalogues and Measurement of the isotropic BAO between
  redshift 0.6 and 1.1 for the Emission Line Galaxy Sample
  We present the Emission Line Galaxy (ELG) sample of the extended Baryon
Oscillation Spectroscopic Survey (eBOSS) from the Sloan Digital Sky Survey IV
Data Release 16 (DR16). After describing the observations and redshift
measurement for the 269,243 observed ELG spectra over 1170 deg$^2$, we present
the large-scale structure catalogues, which are used for the cosmological
analysis. These catalogues contain 173,736 reliable spectroscopic redshifts
between 0.6 and 1.1, along with the associated random catalogues quantifying
the extent of observations, and the appropriate weights to correct for
non-cosmological fluctuations. We perform a spherically averaged baryon
acoustic oscillations (BAO) measurement in configuration space, with density
field reconstruction: the data 2-point correlation function shows a feature
consistent with that of the BAO, providing a 3.2-percent measurement of the
spherically averaged BAO distance $D_V(z_{\rm eff})/r_{\rm drag} = 18.23\pm
0.58$ at the effective redshift $z_{\rm eff}=0.845$.
