Building visual summaries of clusters of trajectories

A big problem in analysis of movement data (trajectories of moving agents) is how to visualize clusters of trajectories so as to have an overview of all clusters and to be able to compare different clusters. Clusters of trajectories are not disjoint in space but intersect and overlap. Hence, they need to be shown separately in multiple small displays. Such displays can be legible only if the clusters are presented in a schematized form. We suggest a method for building schematic representations of clusters of trajectories. The method transforms trajectories into aggregate flows between areas. The areas are automatically defined on the basis of the spatial distribution of the characteristic points from the trajectories. We use numeric measures of the abstraction quality and techniques for controlling the quality.