1. A computer-implemented system for grafting cluster spines, comprising: a spine module to obtain cluster spines, each cluster spine comprising two or more clusters of documents; a vector module to generate a score vector for each of the cluster spines based on the documents within the clusters for that spine; a comparison module to compare the score vectors of the cluster spines; a placement module to place in a display those cluster spines that are sufficiently dissimilar from the other cluster spines based on the comparison; and a grafting module to graft at least one remaining cluster spine onto one of the displayed spines such that no overlap of the placed spine and the remaining spine occurs.