Short geodesics and end invariants

This expository article discusses some connections between the geometry of a hyperbolic 3-manifold homotopy-equivalent to a surface, and the combinatorial properties of its end invariants. In particular a necessary and sufficient condition is stated for the manifold to have arbitrarily short geodesics, in terms of a sequence of coefficients called subsurface projection distances, which are analogous in some ways to continued-fraction coefficients. (The proof of sufficiency appeared in math.GT/9907070)