Abstract A methodology for analyzing geographic data using the techniques of: (1) qualitative geometric abstraction; and (2) ontological analysis of geographic features is described. The first technique is a bottom-up approach to extract qualitative spatial relations from geographic representations (raster or vector) while the second technique is a top-down approach to determine which qualitative relations can possibly hold between the parts of the geographic features. The process of analyzing geographic data includes the extraction of both the features and the qualitative relations among features. These qualitative relations are then used to classify the geographic features within the “space” of ontological possibilities. In this article bays in Wisconsin and their cartographic representation are used as a running example and the subject of a case study.