On the Geometric Thickness of 2-Degenerate Graphs

Authors Rahul Jain , Marco Ricci , Jonathan Rollin , André Schulz

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Rahul Jain
  • FernUniversität in Hagen, Germany
Marco Ricci
  • FernUniversität in Hagen, Germany
Jonathan Rollin
  • FernUniversität in Hagen, Germany
André Schulz
  • FernUniversität in Hagen, Germany

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Rahul Jain, Marco Ricci, Jonathan Rollin, and André Schulz. On the Geometric Thickness of 2-Degenerate Graphs. In 39th International Symposium on Computational Geometry (SoCG 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 258, pp. 44:1-44:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


A graph is 2-degenerate if every subgraph contains a vertex of degree at most 2. We show that every 2-degenerate graph can be drawn with straight lines such that the drawing decomposes into 4 plane forests. Therefore, the geometric arboricity, and hence the geometric thickness, of 2-degenerate graphs is at most 4. On the other hand, we show that there are 2-degenerate graphs that do not admit any straight-line drawing with a decomposition of the edge set into 2 plane graphs. That is, there are 2-degenerate graphs with geometric thickness, and hence geometric arboricity, at least 3. This answers two questions posed by Eppstein [Separating thickness from geometric thickness. In Towards a Theory of Geometric Graphs, vol. 342 of Contemp. Math., AMS, 2004].

Subject Classification

ACM Subject Classification
  • Mathematics of computing → Graph theory
  • Theory of computation → Randomness, geometry and discrete structures
  • Degeneracy
  • geometric thickness
  • geometric arboricity


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