Galactic cold cores III. General cloud properties
  We examine the cloud structure around the Planck detections in 71 fields
observed with the Herschel SPIRE instrument. We wish to determine the general
physical characteristics of the fields and to examine the morphology of the
clouds where the cold high column density clumps are found. We derive colour
temperature and column density maps of the fields. We examine the infrared
spectral energy distributions of the main clumps. The clouds are categorised
according to their large scale morphology. With the help of recently released
WISE satellite data, we look for signs of enhanced mid-infrared scattering
(coreshine), an indication of growth of the dust grains, and examine the star
formation activity associated with the cold clumps. The mapped clouds have
distances ranging from ~100pc to several kiloparsecs and cover a range of sizes
and masses from cores of less than 10 solar masses to clouds with masses in
excess of 10000 solar mass. Most fields contain some filamentary structures and
in about half of the cases a filament or a few filaments dominate the
morphology. In one case out of ten, the clouds show a cometary shape or have
sharp boundaries indicative of compression by an external force. The width of
the filaments is typically ~0.2-0.3pc. However, there is significant variation
from 0.1pc to 1pc and the estimates are sensitive to the methods used and the
very definition of a filament. Enhanced mid-infrared scattering, coreshine, was
detected in four clouds with six additional tentative detections. The cloud
LDN183 is included in our sample and remains the best example of this
phenomenon. About half of the fields are associated with active star formation
as indicated by the presence of mid-infrared point sources. The mid-infrared
sources often coincide with structures whose sub-millimetre spectra are still
dominated by the cold dust.
