Area and perimeter distribution of a surface in two dimensions

We consider the number of configurations of a surface in two dimensions that has a prescribed length and encloses a prescribed perimeter with respect to a baseline. An approximate analytical treatment in a semi--continuum compares favourably with results from an exact algorithm for the discrete lattice. This work is relevant for finding the entropy associated with macroscopic configurations of such systems as domain growth problems, evaporation--deposition problems, membrane physics, or polymer physics.