  A film-like or a thread-like system is a system such that one of its
constituting homogeneous phases has a constant thickness $\delta$ or a constant
normal section of largest diameter $\delta$. The stick probability function of
this phase, in the limit $\delta \to 0$, naturally leads to the definition of
the correlation function (CF) of a surface or a curve. This CF fairly
approximates the generating stick probability function in the range of
distances larger than $\delta$. The surface and the curve CFs respectively
behave as $1/r$ and $1/r^2$ as $r \to 0$. In the two cases, this result implies
that small-angle scattering intensities of the relevant samples respectively
behave as $1/q^2$ and $1/q$ in an intermediate range of the scattering vector
$q$ and as $1/q^4$ in the outermost one. One reports the analytic expressions
of the pre-factors of these behaviors. It may happen that a sample looks
thread-like at large scale resolution and film-like at smaller one. The surface
and the curve CFs have explicitly been evaluated for some simple geometrical
shapes. Besides, it is also reported the algebraic expression of the circular
cylinder CF in terms of two elliptic integral functions, and it is shown that
the limits of this CF, as the height or the radius of the cylinder approaches
to zero, coincide with the CF of a disk or a linear segment, respectively.
