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An information visualization display can hold a certain amount of data points before it gets crowded. One way to solve this problem with larger and larger data sets is to create aggregates. An aggregate is a group of data points that is used as summarization. The aggregates are used in the visualization instead of all the data points to simplify the display.
The concept of aggregation can be used together with the Snap-Together Visualization to tightly couple and coordinate different displays.
This paper presents a case study with incident data from the highways in Maryland where both aggregation and coupled displays are used. More than ten different prototypes with different kinds of aggregates have been developed and analyzed. Recommendations and advice regarding the use of aggregation will be given to people working with transportation systems, and to developers of coupled displays and visualization applications. Some general principles about aggregates found during the development process will also be presented.