A (Hasse) diagram of a finite partially ordered set (poset) P will be called
quasiplanar if for any two incomparable elements u and v, either v is on the
left of all maximal chains containing u, or v is on the right of all these
chains. Every planar diagram is quasiplanar, and P has a quasiplanar diagram
iff its order dimension is at most 2. A finite lattice is slim if it is
join-generated by the union of two chains. We are interested in diagrams only
up to similarity. The main result gives a bijection between the set of the
(similarity classes of) finite quasiplanar diagrams and that of the (similarity
classes of) planar diagrams of finite, slim, semimodular lattices. This
bijection allows one to describe finite posets of order dimension at most 2 by
finite, slim, semimodular lattices, and conversely. As a corollary, we obtain
that there are exactly (n-2)! quasiplanar diagrams of size n.Comment: 19 pages, 3 figure