Composite of optical data (image courtesy of Roberto Bernal Andreo; deepskycolors.com) overlayed with Planck-Herschel column density measurements of Orion A in green. Approximate positions of noteworthy objects and regions are marked and labeled. On top, a histogram (note the logarithmic scaling) shows the number of references for all objects in the SIMBAD database at a given galactic longitude with a 3 arcmin bin size. We see an extreme gradient in attention paid to the various portions of the cloud, with the peak coinciding with M42 and the ONC. Prominent objects (e.g., the V380/HH 1−2 region) produce a local spike in the reference histogram whereas the bulk of the molecular cloud has been studied in comparatively few articles. The coordinates of L1647 in the SIMBAD database (l = 212.13, b = −19.2) do not match the original publication (l = 214.09, b = −20.04).