Thematic information of a long document(i.e.,a novel) can be multi-faceted:an interleaving of multiple topics,a sequential evolution of a set of themes,or a crossing superimposition of topics and themes.Conventional topic-based visualization approaches are inefficient to capture this complicated thematic structure.This paper introduces a novel topic-based model,called the topic hypergraph,that characterizes the thematic structure of a long document with a hypergraph representation.Each hypergraph node represents a unique document piece,and encodes its theme as a composition of multiple topics.Two types of relationships among nodes are modeled:an edge that connects two consecutive themes to present their sequential transition,and a hyperedge that encodes a topic.The new representation is essentially a 2D reformulation of the linear streamgraph representation,and can be adaptive by constructing a multi-level hierarchy.We design a suite of visualization and interaction tools to allow users to interactively analyze the theme evolution,theme diversities,and topic interleaving.Our approach is also suitable for comparing multiple long documents.