Applying Gestalt principles to animated visualizations of network data

Graphs are a commonly used data structure for representing relational information. Drawings of these structures, as node and link diagrams, can provide a useful visualization of the underlying abstract data. This makes drawings of graphs a useful tool in information visualization. Indeed graph drawing has been applied in many application areas including software engineering, knowledge management and for depicting communication networks. The spatial layout can help the user build up a cognitive model or 'mental map' of the information structure. Many automatic algorithms for producing drawings of a graph have been implemented. In many domains it is also common for the underlying information to be dynamic and this means the graph drawing must be updated. Unfortunately, even small changes to the underlying data can result in dramatic changes to the final drawing and this means the user may totally lose their previous 'mental map'. Animation between the two versions of the layout is one approach that can assist the user to make the transition between the two drawings. We have been examining how to apply the Gestalt principles of organisation to this animation phase. The aim is to assist the user in understanding the structural and visual changes that have occurred in the layout. Results of that work are described with relevant examples.