In this paper, we study
some topological properties of rational polynomial maps f : ℂ2→ ℂ. One can extend
f to a map φ : X → ℙ1 where X is a smooth algebraic compactification of ℂ2. The
behaviour of φ on the curve 𝒟 := X ∖ ℂ2 contains all the information on the topology
of f at infinity. We study the relationship between the so-called horizontal
componentes of 𝒟, i.e., irreducible components D of 𝒟 such that ϕ|D is
surjective.