In this paper, we present the knowledge-based system ROSA working on spatial and functional organizations of farms in agronomy. The goal of this system is twofold: validation of the domain model and analysis of the functional organization with respect to the spatial organization of farms. First, we propose and detail a model of the domain based on the so-called ``spatial organization graph'' (sog). Then, we show how description logics are used to represent and to manipulate these spatial organization graphs. The reasoning in the ROSA system is mainly based on case-based reasoning, and involves also concept classification and spatial reasoning. Finally, we describe the manipulation of spatial organization graphs using case-based reasoning, and we discuss the overall approach before concluding.