Beyond-planarity: A generalization of the planarity concept in graph drawing

• Applicant: Professor Dr. Michael Kaufmann, Ph.D.
• Subject Area: Theoretical Computer Science
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 364468267

The research field of graphs beyond planarity has been developed in recent years tremendously; evidence are several workshops and Dagstuhl seminars with this particular topic, as well as a survey book that will be published soon. In the first proposal in 2017, we gave a wide collection of research tasks in various directions. Meanwhile, we contributed in several directions; we summarized this in the progress report. However, we have also identified several new interesting research challenges and directions that we want to follow.1. Classification: We want robust definitions that are also parametrizable (fan-planar -> k-fan-planar, k-gap-planar -> (k,l)-gap-planar). We also want clear hierarchies between different graph classes. We expect to find new classes that complete the hierarchic structure. The classification will also be accompanied by combinatorial and algorithmic analyses on structural properties and parameters (e.g., low degree, girth etc) of the considered classes. 2. Layout: During the first project phase, we observed that the work on layout algorithms for graphs beyond planarity is very limited. The main reason for this is that the known techniques cannot be adopted so easily. Therefore, during the second project phase we will put our main focus on this aspect. For example for the standard approach to compute an appropriate topological embedding, and then a corresponding geometric embedding, both steps are challenging for the case of graphs beyond planarity and provide a considerable portion of risk in the project. To find algorithms which are practically applicable, we plan to provide fast exponential-time algorithms, maybe refined by parametrization, or efficient heuristics that can produce close-to-optimal layouts. It is definitely a far-from-trivial task to find corresponding requirements for more complex classes. Only elementary results are currently known mostly limited to the class of 1-planar graphs.3. Dissemination: By organizing meetings with other groups, we will develop the field further keeping the topic of beyond planarity as a central topic in regular workshops such as GNV in Heiligkreuztal, BWGD in Bertinoro and Dagstuhl. At such workshops, we find new insights by combining forces with people from combinatorial graph theory and computational geometry but also from algorithmic graph theory (e.g., Pach, T\'oth, Hoffmann, Speckmann). In 2016 and 2019, the applicant co-organized two Dagstuhl seminars on beyond planarity. A new edition of this successful Dagstuhl seminar is currently under consideration. As a side note, we further mention that in 2021 our group will be organizing the 29th Symposium of Graph Drawing and Network Visualization in Tübingen, a great honor and appreciation of our work in the field.

• DFG Programme: Research Grants