We present a new and scalable technique to explore surveillance videos by scatter/gather browsing of trajectories of moving objects. The proposed approach facilitates interactive clustering of trajectories by an effective way of cluster visualization that we term schematic summaries. This novel visualization illustrates cluster summaries in a schematic, non-photorealistic style. To reduce visual clutter, we introduce the trajectory bundling technique. The fusion of schematic summaries and user interaction leads to efficient hierarchical exploration of video data. Examples of different browsing scenarios demonstrate the effectiveness of the proposed method.