  We implement a new observational method for mapping the aliphatic hydrocarbon
content in the solid phase in our Galaxy, based on spectrophotometric imaging
of the 3.4 $\mu$m absorption feature from interstellar dust. We previously
demonstrated this method in a field including the Galactic Centre cluster. We
applied the method to a new field in the Galactic centre where the 3.4 $\mu$m
absorption feature has not been previously measured and we extended the
measurements to a field in the Galactic plane to sample the diffuse local
interstellar medium, where the 3.4 $\mu$m absorption feature has been
previously measured. We have analysed 3.4 $\mu$m optical depth and aliphatic
hydrocarbon column density maps for these fields. Optical depths are found to
be reasonably uniform in each field, without large source-to-source variations.
There is, however, a weak trend towards increasing optical depth in a direction
towards $b=0^{\circ}$ in the Galactic centre. The mean value of column
densities and abundances for aliphatic hydrocarbon were found to be about
several $\rm \times 10^{18} \, cm^{-2}$ and several tens $\times 10^{-6}$,
respectively for the new sightlines in the Galactic plane. We conclude that at
least 10-20% of the carbon in the Galactic plane lies in aliphatic form.
