Comparing the Readability of the Force-Directed and Orthogonal Graph Layout

Abstract: The readability of a graph layout is defined as the efficiency of finding information on that graph, and is measured as the completion time and correctness when performing a task with that layout. Hence, the more readable a layout is, the more efficient a user becomes. As many application areas, such as fraud detection and cyber security uses graph visualizations, it has become essential that visualization designers should judge graph layouts by their readability instead of their aesthetic appeal in order to achieve maximum efficiency. In this study the readability of two well known graph layouts, the forcedirected and orthogonal layout, were compared and evaluated using four topology based tasks defined by the Task Taxonomy of Graph Visualization. To accomplish this, a user study based on the works of three previous evaluation studies was designed and conducted online with 11 participants. The results indicate that the force-directed layout had significantly better average completion times for tasks which required to find adjacent nodes, and equal average correctness for all tasks, assuming that the layouts provide incident-edge-highlighting. The differences in readability are argued to be caused by the edge shape of the orthogonal layout. This argument is supported by the Gestalt Principles and previous work. Studies such as this one could be beneficial in the design process of future graph visualizations in an effort to improve the efficiency of its usage.