We investigate direct manipulation of graphical encodings as a method for interacting with visualizations. There is an increasing interest in developing visualization tools that enable users to perform operations by directly manipulating graphical encodings rather than external widgets such as checkboxes and sliders. Designers of such tools must decide which direct manipulation operations should be supported, and identify how each operation can be invoked. However, we lack empirical guidelines for how people convey their intended operations using direct manipulation of graphical encodings. We address this issue by conducting a qualitative study that examines how participants perform 15 operations using direct manipulation of standard graphical encodings. From this study, we 1) identify a list of strategies people employ to perform each operation, 2) observe commonalities in strategies across operations, and 3) derive implications to help designers leverage direct manipulation of graphical encoding as a method for user interaction.
In total participants employed 203 strategies to perform 15 different operations. We first sketched out each participant's strategy and grouped these sketches into 48 independent categories based on their similarities. Each sketch belongs only to one of the identified categories and all categories are exclusive. We then independently named each category of strategies (e.g.,``Stack points vertically'') and counted the total number of sketches ineach category. The interactive table below shows in rows the 15 operations participants performed during the study, and in columns the 48 strategies we identified. Each cell shows the number of times participants used the strategy in column to perform the operation in row. The higher the value in a cell, the darker the background of the cell. Hovering on each strategy shows its description.