The SDSS-IV MaNGA Sample: Design, Optimization, and Usage Considerations
  We describe the sample design for the SDSS-IV MaNGA survey and present the
final properties of the main samples along with important considerations for
using these samples for science. Our target selection criteria were developed
while simultaneously optimizing the size distribution of the MaNGA integral
field units (IFUs), the IFU allocation strategy, and the target density to
produce a survey defined in terms of maximizing S/N, spatial resolution, and
sample size. Our selection strategy makes use of redshift limits that only
depend on i-band absolute magnitude ($M_i$), or, for a small subset of our
sample, $M_i$ and color (NUV-i). Such a strategy ensures that all galaxies span
the same range in angular size irrespective of luminosity and are therefore
covered evenly by the adopted range of IFU sizes. We define three samples: the
Primary and Secondary samples are selected to have a flat number density with
respect to $M_i$ and are targeted to have spectroscopic coverage to 1.5 and 2.5
effective radii (Re), respectively. The Color-Enhanced supplement increases the
number of galaxies in the low-density regions of color-magnitude space by
extending the redshift limits of the Primary sample in the appropriate color
bins. The samples cover the stellar mass range $5\times10^8 \leq M_* \leq
3\times10^{11} M_{\odot}$ and are sampled at median physical resolutions of
1.37 kpc and 2.5 kpc for the Primary and Secondary samples respectively. We
provide weights that will statistically correct for our luminosity and
color-dependent selection function and IFU allocation strategy, thus correcting
the observed sample to a volume limited sample.
