Chimani, Markus, and Philipp Hungerländer. “Multi-Level Verticality Optimization: Concept, Strategies, and Drawing Scheme”. Journal of Graph Algorithms and Applications 17, no. 3 (March 1, 2013): 329–362. Accessed May 1, 2025. https://www.jgaa.info/index.php/jgaa/article/view/paper296.