It is well known that bounded diameter planar graphs have bounded treewidth (e.g. see this). Does the converse hold? That is, is every planar bounded treewidth graph the (induced?) subgraph of a bounded diameter planar graph?

I am interested in a proof sketch/reference if this is true or a counterexample if this is false.

Note1: David's correct answer below is in the negative. In its light can we modify the question to read: Are k-outerplanar graphs subgraphs of simultaneously bounded diameter and bounded genus graphs?

Note2: David further indicates (correctly) that the nested triangles graph cannot be made bounded tree-width even at the expense of increasing the genus to a constant.

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    $\begingroup$ I'd recommend posting your followup as a separate question that references this one (since this question is essentially resolved) $\endgroup$ – Suresh Venkat Jun 12 '13 at 0:57

No: see the nested triangles graph. It has bounded treewidth (more strongly, bounded pathwidth and bandwidth) but cannot be augmented to have bounded diameter while preserving planarity.

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  • $\begingroup$ A followup question: what if we replace planar by bounded genus above? I.e. k-outerplanar graphs are subgraphs of bounded diameter bounded genus graphs? $\endgroup$ – SamiD Jun 12 '13 at 0:29
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    $\begingroup$ Do you have a way of reducing the diameter of the nested triangles graph below linear by adding edges while keeping the genus bounded? $\endgroup$ – David Eppstein Jun 13 '13 at 0:31
  • $\begingroup$ No. You are correct, I can't think of such a way. $\endgroup$ – SamiD Jun 13 '13 at 11:07

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