  We present baryon acoustic oscillation (BAO) scale measurements determined
from the clustering of 1.2 million massive galaxies with redshifts 0.2 < z <
0.75 distributed over 9300 square degrees, as quantified by their
redshift-space correlation function. In order to facilitate these measurements,
we define, describe, and motivate the selection function for galaxies in the
final data release (DR12) of the SDSS III Baryon Oscillation Spectroscopic
Survey (BOSS). This includes the observational footprint, masks for image
quality and Galactic extinction, and weights to account for density
relationships intrinsic to the imaging and spectroscopic portions of the
survey. We simulate the observed systematic trends in mock galaxy samples and
demonstrate that they impart no bias on baryon acoustic oscillation (BAO) scale
measurements and have a minor impact on the recovered statistical uncertainty.
We measure transverse and radial BAO distance measurements in 0.2 < z < 0.5,
0.5 < z < 0.75, and (overlapping) 0.4 < z < 0.6 redshift bins. In each redshift
bin, we obtain a precision that is 2.7 per cent or better on the radial
distance and 1.6 per cent or better on the transverse distance. The combination
of the redshift bins represents 1.8 per cent precision on the radial distance
and 1.1 per cent precision on the transverse distance. This paper is part of a
set that analyses the final galaxy clustering dataset from BOSS. The
measurements and likelihoods presented here are combined with others in Alam et
al. (2016) to produce the final cosmological constraints from BOSS.
