The Digital Library (DL) field is one of the most promising areas of application for information visualization technology. In this paper, we propose a visual user interface tool kit for digital libraries, to deliver an overview of document sets, with support for interactive direct manipulation. Our system, Citiviz, employs a dynamic hyperbolic tree to display hierarchical relationships among documents, based on where their topics fit into the ACM classification system. Also, Citiviz provides an interactive, animated 2-dimensional scatter plot. With it, users may gain insight by changing various parameters, or may directly jump to a particular document based on its label or location. According to a preliminary evaluation, our system shows advantages in performance and user preference relative to traditional text based DL web interfaces.