Drill-down and Roll-up

The two basic hierarchical operations when displaying data at multiple levels of aggregations are the ``drill-down'' and ``roll-up'' operations. Drill-down refers to the process of viewing data at a level of increased detail, while roll-up refers to the process of viewing data with decreasing detail.

Our system provides smooth and continuous level-of-detail control in all drilling operations. The control parameter is based on a measure of cluster sizes (ref. section 5.1).

Selective Drill-down and Roll-up

We also coupled our drilling operations with brushing. Our system permits selective drill-down and roll-up of the brushed and non-brushed region independently. This flexibility is important as it allows the viewing of a subset of elements in varying levels of detail in relation to elements outside the subset.