  The first detections of gravitational waves from binary neutron star mergers
with advanced LIGO and Virgo observatories are anticipated in the next five
years. These detections could pave the way for multi-messenger
gravitational-wave (GW) and electromagnetic (EM) astronomy if GW triggers are
successfully followed up with targeted EM observations. However, GW sky
localization is relatively poor, with expected localization areas of ~10--100
square degrees; this presents a challenge for following up GW signals from
compact binary mergers. Prioritizing wide-field follow-ups based on the
probability of successful imaging is important when it is impossible to tile
the entire gravitational-wave localization region.
  Galaxy catalogs were effective at narrowing down regions of the sky to search
in initial attempts at joint GW/EM observations. The next generation of GW
detectors will have a ten-fold increase in range thereby increasing the
expected number of galaxies per unit solid angle a thousand-fold. As an
additional complication, catalogs may be highly incomplete.
  We show how to quantify the advantages of using galaxy catalogs as a function
of only two parameters: the three-dimensional volume within the field of view
of a telescope after accounting for the GW distance measurement uncertainty,
and the fraction of the GW sky localization uncertainty region that can be
followed up. We find that the use of galaxy catalogs can improve success rates
by ~10% to a factor of 4 relative to follow-up strategies that do not utilize
such catalogs for the scenarios we considered. We determine that catalogs with
a 75% completeness perform comparably to complete catalogs in most cases, while
33%-complete catalogs can lead to lower follow-up success rates than complete
catalogs for small fields of view, though still providing an advantage over
strategies that do not use a catalog at all.
