  The latest generation of high-angular-resolution unbiased Galactic plane
surveys in molecular-gas tracers are enabling the interiors of molecular clouds
to be studied across a range of environments. The CHIMPS survey simultaneously
mapped a sector of the inner Galactic plane, within 27.8 < l < 46.2 deg and |b|
< 0.5 deg, in 13CO and C18O (3-2) at 15 arcsec resolution. The combination of
CHIMPS data with 12CO (3-2) data from the COHRS survey has enabled us to
perform a voxel-by-voxel local-thermodynamic-equilibrium analysis, determining
the excitation temperature, optical depth, and column density of 13CO at each
l,b,v position. Distances to discrete sources identified by FellWalker in the
13CO (3-2) emission maps were determined, allowing the calculation of numerous
physical properties of the sources, and we present the first source catalogues
in this paper. We find that, in terms of size and density, the CHIMPS sources
represent an intermediate population between large-scale molecular clouds
identified by CO and dense clumps seen in dust emission, and therefore
represent the bulk transition from the diffuse to the dense phase of molecular
gas. We do not find any significant systematic variations in the masses, column
densities, virial parameters, excitation temperature, or the turbulent pressure
over the range of Galactocentric distance probed, but we do find a shallow
increase in the mean volume density with increasing Galactocentric distance. We
find that inter-arm clumps have significantly narrower linewidths, and lower
virial parameters and excitation temperatures than clumps located in spiral
arms. When considering the most reliable distance-limited subsamples, the
largest variations occur on the clump-to-clump scale, echoing similar recent
studies that suggest that the star-forming process is largely insensitive to
the Galactic-scale environment, at least within the inner disc.
