  This article introduces the generic Document Towers paradigm, visualization,
and software for visualizing the structure of paginated documents, based on the
metaphor of documents-as-architecture. The Document Towers visualizations
resemble three-dimensional building models and represent the physical
boundaries of logical (e.g., titles, images), semantic (e.g., topics, named
entities), graphical (e.g., typefaces, colors), and other types of information
with spatial extent as a stack of rooms and floors. The software takes as input
user-supplied JSON-formatted coordinates and labels of document entities, or
extracts them itself from ALTO and InDesign IDML files. The Document Towers
paradigm and visualization enable information systems to support information
behaviors other than goal-oriented searches. Visualization encourages
exploration by generating panoramic overviews and fostering serendipitous
insights, while the use of metaphors assists with comprehension of the
representations through the application of a familiar cognitive model. Document
Towers visualizations also provide access to types of information other than
textual content, specifically by means of their physical structure, which
corresponds to the material, logical, semantic, and contextual aspects of
documents. Visualization renders documents transparent, making the invisible
visible and facilitating analysis at a glance and without the need for physical
manipulation. Keyword searches and other language-based interactions with
documents must be clearly expressed and will return only answers to questions
asked; by contrast, visual observation is well suited to fuzzy goals and
uncovering unexpected aspects of the data.
