Planar st-graphs are used in a number of different application fieldsin the sciences, but also in industry. So far, mainly node-link-basedlayouts have been used to visualize such graphs especially in theGraph Drawing community. One drawback of these standard layoutsis their high consumption of space. In Information Visualization,there exist visualization techniques for graphs which achieveconsiderable space savings, such as matrix-based approaches. Inthis work, we present a novel space-filling representation to visualizeplanar st-graphs.