Method and apparatus for displaying and navigating data organized in the form of a graph structure (hierarchy or network) is presented. The invention has application for displaying a system of interconnected nodes such as a graph, a network, an organizational chart, a flowchart etc. wherein data or information is associated with nodes of the system. A user interface is implemented as an ActiveX control having a viewer component for displaying and navigating graph structur (for example a data mining model over data records or a directory structure over a set of files). The viewer component updates the contents of related windows that display different aspects of the components (nodes) of the data structure. A thumbnail window presents the user with an overview of the data structure. A layout window presents a more detailed view of part of the graph structure. Other windows display context and detailed properties associated with particular selected nodes. One instance of the invention is used for displaying structure of a database classifier which organizes data in a tree. A tree viewer maintains a depiction of the entire graph (or tree) in the Thumbnail window and depicts a detailed portion of the graph in a larger layout window. The user can move the mouse pointer over either the thumbnail or the layout window and by mouse actuated inputs can control the manner in which the window depicts the tree structure. Color coding of properties of the structure being displayed, along with auxiliary detail windows for displaying values and histograms, can be used to quickly navigate a large structure and locates zones of interest within it.