  We construct the largest curved-sky galaxy weak lensing mass map to date from
the DES first-year (DES Y1) data. The map, about 10 times larger than previous
work, is constructed over a contiguous $\approx1,500 $deg$^2$, covering a
comoving volume of $\approx10 $Gpc$^3$. The effects of masking, sampling, and
noise are tested using simulations. We generate weak lensing maps from two DES
Y1 shear catalogs, Metacalibration and Im3shape, with sources at redshift
$0.2<z<1.3,$ and in each of four bins in this range. In the highest
signal-to-noise map, the ratio between the mean signal-to-noise in the E-mode
and the B-mode map is $\sim$1.5 ($\sim$2) when smoothed with a Gaussian filter
of $\sigma_{G}=30$ (80) arcminutes. The second and third moments of the
convergence $\kappa$ in the maps are in agreement with simulations. We also
find no significant correlation of $\kappa$ with maps of potential systematic
contaminants. Finally, we demonstrate two applications of the mass maps: (1)
cross-correlation with different foreground tracers of mass and (2) exploration
of the largest peaks and voids in the maps.
