A Time-Windowed Data Structure for Spatial Density Maps

Annika Bonerath, Benjamin Niedermann, Jim Diederich, Yannick Orgeig, Johannes Oehrlein, Jan-Henrik Haunert

Geoinformation, University of Bonn, Germany

The visualization of spatio-temporal data helps researchers understand global processes such as animal migration. In particular, interactively restricting the data to different time windows reveals new insights into the short-term and long-term changes of the research data. Inspired by this use case, we consider the visualization of point data annotated with time stamps. We pick up classical, grid-based density maps as the underlying visualization technique and enhance them with an efficient data structure for arbitrarily specified time-window queries.

We invite the reader to try out our prototypical implementation for the following three scenarios.

Bird Migration

>> Demo <<


>> Demo <<


>> Demo <<

The running time of the queries is logarithmic in the total number of points and linear in the number of actually colored cells. In experiments on real-world data we show that the data structure answers time-window queries within milliseconds, which supports interactive exploration of large point sets. Further, the data structure can be used to visualize additional decision problems, e.g., it can answer queries whether the sum or maximum of additional weights given with the points exceed a certain threshold. We have defined the data structure general enough to also support multiple thresholds expressed by different colors.

Annika Bonerath or Benjamin Niedermann

We obtained the map tiles by Stamen Design, under CC BY 3.0, and the map data by OpenStreetMap, under ODbL. For the visualization we use the implementation provided by Open Layers, under 2-clause BSD License.