Composite all-sky map of neutral hydrogen column density (N_HI), formed from the Leiden/Dwingeloo HI survey data (Hartmann & Burton 1997) and the composite N_HI map of Dickey and Lockman (1990). The two datasets are not matched in sensitivity or resolution: note that discontinuities exist in the constructed composite map. A pixel mask is provided to indicate which dataset was used for each location on the sky. Hartmann & Burton provide a velocity integrated (-450 km/s %3C V_lsr %3C +400 km/s) HI brightness temperature map in Galactic coordinates, sampled every 0.5 degrees. This entire data set was converted to N_HI by multiplying by their factor of 1.8224e18 K km s-1 cm-2 and then interpolated to pixel centers appropriate for HEALPix Nside. Original acknowledgement for data: We acknowledge the use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA), part of the High Energy Astrophysics Science Archive Center (HEASARC). HEASARC/LAMBDA is a service of the Astrophysics Science Division at the NASA Goddard Space Flight Center.