On the Order Dimension of Outerplanar Maps

TL;DR

This paper explores the order dimension of vertex-edge-face and vertex-face posets of planar maps, identifying conditions for when this dimension is at most three, especially in outerplanar maps, and provides algorithms for recognition.

Contribution

It characterizes when the order dimension of certain posets of planar maps is at most three, linking it to outerplanarity and oriented colorings, and introduces a linear time recognition algorithm.

Findings

Maps with $K_4$-subdivisions have dimension 4.

Maps with $K_{2,3}$-subdivisions have dimension 4.

Outerplanar maps with certain properties can be recognized via a linear time algorithm.

Abstract

Schnyder characterized planar graphs in terms of order dimension. Brightwell and Trotter proved that the dimension of the vertex-edge-face poset $\Pvef{M}$ of a planar map $M$ is at most four. In this paper we investigate cases where $\dim(\Pvef{M}) \leq 3$ and also where $\dim(\Qvf{M}) \leq 3$; here $\Qvf{M}$ denotes the vertex-face poset of $M$. We show: - If $M$ contains a $K_4$-subdivision, then $\dim(\Pvef{M}) = \dim(\Qvf{M}) = 4$. - If $M$ or the dual $M^*$ contains a $K_{2,3}$-subdivision, then $\dim(\Pvef{M}) = 4$. Hence, a map $M$ with $\dim(\Pvef{M}) \leq 3$ must be outerplanar and have an outerplanar dual. We concentrate on the simplest class of such maps and prove that within this class $\dim(\Pvef{M}) \leq 3$ is equivalent to the existence of a certain oriented coloring of edges. This condition is easily checked and can be turned into a linear time algorithm returning a 3-realizer. Additionally, we prove that if $M$ is 2-connected and $M$ and $M^*$ are outerplanar, then $\dim(\Qvf{M}) \leq 3$. There are, however, outerplanar maps with $\dim(\Qvf{M}) = 4$. We construct the first such example.