Visualizing very large layered graphs with quilts

Traditional node-link depictions of layered graphs such as flow charts and process or genealogy diagrams are in widespread use. Layers emerge from applied context (e.g. process stages or familial generations), or are inserted to improve visual clarity. However for many applications these diagrams quickly lose their utility as graph complexity grows. Layout algorithms such as crossing minimizers can preserve utility for larger graphs, but also quickly reach their limits. We introduce quilting, an interactive, matrix-based depiction for very large layered graphs that remains useful even when optimized node and link depictions have become unintelligible. We demonstrate quilting using an activity-based management (ABM) application that must depict layered graphs with thousands or even hundreds of thousands of nodes. Unlike node-link depictions, quilts depict 500-node graphs quite clearly. On typical desktop displays, quilts depicting larger graphs must be summarized.