The Affordance of Law. Sliding Treemaps browsing Hierarchically Structured Data on Touch Devices

Sifting through the flood of documents today available and making sense of them is an ever-growing challenge of our time. Visualization is offering new ways to navigate through large sets of documents, mainly through graphs that intuitively depict textual entities (documents or parts thereof) and relations tying them. A relevant issue is that graphs can be smoothly used, especially in desktop environments. The small size of tablets’ and smartphones’ screens makes it difficult to simply port graph visualizations from desktop to mobile devices, just as the use of the latter is growing for browsing and reading texts. In the light of the above, a challenge is seamlessly merging abstraction power offered by visualization, information retrieval, and the access to texts. This paper presents a Human-Computer Interaction strategy integrating mobile devices (for visualization-based, high-level and intuitive interaction with data and their relations) and desktop computers (for full-text reading). We focus on Sliding Treemap, a visualization designed to render graph-like (hierarchical, relational) structures on mobile touch devices. The solution, suitable to be applied also in other domains, has been designed based on the needs of the legal domain, which is "highly textual" and still rather unfamiliar with visualization techniques. Sliding Treemap has been developed in the prototype of a cross-platform app using as testbed the catalogue of the European Court of Justice Library, and sets of heterogeneous legal sources from the Italian legal system