Linked from
The 12 pages that link to Euclidean plane, each with the reason it gives.
Riemannian manifoldBroader topic: It is the simplest complete example of a Riemannian manifold.
TessellationNarrower topic: Ordinary planar tessellation concerns coverings of this flat space.
Geometric constructionNarrower topic: Classical construction operations take place in this plane.
Sylvester–Gallai theoremNarrower topic: The stated theorem concerns finite point sets in this plane.