  We calculated the 3D distribution of the area expansion factors in a
potential magnetic field extrapolated from the high-resolution
\textit{Hinode}/SOT magnetogram of a quiescent active region NOAA 11482.
Retaining only closed loops within the computational box, we show that the
distribution of area expansion factors show significant structure. Loop-like
structures characterized by locally lower values of the expansion factor are
embedded in a smooth background. These loop-like flux-tubes have squashed
cross-sections and expand with height. The distribution of the expansion
factors show overall increase with height, allowing an active region core
characterized by low values of the expansion factor to be distinguished. The
area expansion factors obtained from extrapolation of the SOT magnetogram are
compared to those obtained from an approximation of the observed magnetogram by
a series of 134 submerged charges. This approximation retains the general flux
distribution in the observed magnetogram, but removes the small-scale structure
in both the approximated magnetogram and the 3D distribution of the area
expansion factors. We argue that the structuring of the expansion factor can be
a significant ingredient in producing the observed structuring of the solar
corona. However, due to the potential approximation used, these results may not
be applicable to loops exhibiting twist neither to active regions producing
significant flares.
