Planar and Quasi-Planar Simultaneous Geometric Embedding

Abstract

A simultaneous geometric embedding SGE of two planar graphs G 1 and G 2 with the same vertex set is a pair of straight-line planar drawings Γ1 of G 1 and Γ2 of G 2 such that each vertex is drawn at the same point in Γ1 and Γ2. Many papers have been devoted to the study of which pairs of graphs admit a SGE, and both positive and negative results have been proved. We extend the study of SGE, by introducing and characterizing a new class of planar graphs that makes it possible to immediately extend several positive results that rely on the property of strictly monotone paths. Moreover, we introduce a relaxation of the SGE setting where Γ1 and Γ2 are required to be quasi planar i.e., they can have crossings provided that there are no three mutually crossing edges. This relaxation allows for the simultaneous embedding of pairs of planar graphs that are not simultaneously embeddable in the classical SGE setting and opens up to several new interesting research questions.