Hans Steffen, a prominent Prussian geographer (1865-1936), was hired in 1889 by the Government of Chile as Professor of Geography for the recently formed Pedagogical Institute, with the aim of educating Geography teachers and writing texts to contribute to the institutionalization of national geography. Towards the end of the nineteenth century, when Steffen was already an established professional in Santiago, Chile and Argentina submitted their Andean border litigation to international arbitration. In that context, Steffen was actively involved in preparing the document which the Chilean government would present at the dispute. This article analyzes the geographical practices, ideas, and theories developed by Steffen for the conceptualization and demarcation of the border between Argentina and Chile, by examining the texts (newspapers, didactic books, diplomatic declarations, published conferences) and images (maps, photos, sketches, outlines and field notes) he produced.