  Adsorption at a 1-dimensional planar substrate equipped with a localized
chemical inhomogeneity is studied within the framework of a continuum
interfacial model from the point of view of interfacial morphology and
correlation function properties. Exact expressions for the one-point and
two-point probability distribution functions $P_\Gamma (l_\Gamma)$ and
$P_{\Gamma_1, \Gamma_2}(l_{\Gamma_1},l_{\Gamma_2})$, $l_\Gamma$ being the
interface position above a fixed point $\Gamma$ of the substrate, are derived
for temperature corresponding to the inhomogeneity's wetting transition. It is
demonstrated that in the limit of macroscopic inhomogeneity's size the net
effect of the remaining homogeneous parts of the substrate on the interfacial
morphology above the inhomogeneity is exactly equivalent to appropriate pinning
of the interface at its boundaries. The structure of the average interfacial
morphology and correlation function in this limit are discussed and compared to
earlier results obtained for systems with homogeneous substrate.
