The work of Eugene Romer, founder of Polish geography, was framed by his involvement in the national cause. The Atlas of Poland, a key tool in his political activism, was completed during the First World War under the uncertain circumstances prevailing on the Eastern Front. It focused more on the issue of unification than on boundaries. Skilled in physical geography, Romer made use of a cartographical technique rarely applied to ethnographical maps, that of isopleths. In this article, we address the reasons for this daring innovation and consider Romer's training in the Austrian and German schools of cartography before examining the reception of the atlas by geographers from the different academic backgrounds.