Image Analysis for the History of Cartography: Drawing Conclusions from the Evaluation of Pfyffer's Relief

Digital photogrammetry offers effective and accurate procedures for the preservation and inventory of cultural heritage. In case of twoand three-dimensional products of early mapmaking the application of these methods goes far beyond documentation and visualization: it primarily aims at the derivation of new information. This paper reports on conclusions which can be drawn from the quantitative evaluation of one of the most spectacular relief models in history, the relief of Franz Ludwig Pfyffer constructed between 1750 and 1786. At first, the techniques and results of image-based reconstruction and accuracy analysis of this masterpiece are briefly summarized. Due to the lack of written documentation concerning the relief and its constructor, the virtual Pfyffer's Relief and the products of image processing represent a great potential for research in the history of cartography. Thus, the main focus of the paper is the reconstruction of Pfyffer's surveying procedures and the interpretation of the reached accuracy in context of European mapmaking of that period. The work leads to a new knowledge about the cartographic, spatiotemporal but also social and political aspects of the relief creation. As opposed to the previous assumptions it can be concluded that Pfyffer performed systematic and repetitive triangulation and height measurements. His procedures, instruments and results correspond with the scientific status quo in the last quarter of the 18th century, whereas his area-wide height survey was a pioneering achievement at that time.