  The initial discovery of LIGO on 14 September 2015 was the inspiral merger
and ring-down of the black hole binary at a distance of about 500~Mpc or a
redshift of about 0.1. The search for electromagnetic counterparts for the
inspiral of binary black holes is impeded by coarse initial source
localisations and a lack of a compelling model for the counterpart; therefore,
rapid electromagnetic follow-up is required to understand the astrophysical
context of these sources. Because astrophysical sources of gravitational
radiation are likely to reside in galaxies, it would make sense to search first
in regions where the LIGO-Virgo probability is large and where the density of
galaxies is large as well. Under the assumption that the probability of a
gravitational-wave event from a given region of space is proportional to the
density of galaxies within the probed volume, one can calculate an improved
localisation of the position of the source simply by multiplying the LIGO-Virgo
skymap by the density of galaxies in the range of redshifts. We propose using
the 2-MASS Photometric Redshift Galaxy Catalogue for this purpose and
demonstrate that using it can dramatically reduce the search region for
electromagnetic counterparts.
