Presentation at EuroVis 2012, Vienna, Austria. Find our paper at http://tillnagel.com/wp-content/uploads/2012/06/Nagel-SankeyArcs-EuroVis11.pdf Arc diagrams allow exploring relations and their strength between sequential nodes. Previous solutions suffer from displaying all arcs at the center of a node, which can lead to visual obstruction. We present a new technique, which extends the arc diagram technique by laying out the weighted edges of a node adjacent to each other. The aim of our Sankey Arc technique is to improve clarity, to enable users perceiving and comparing weighted edges in path graphs. The technique is illustrated using a dataset on travel paths in a public transit network.

1. Sankey Arcs – Visualizing
edge weights in path graphs
Till Nagel, Erik Duval, Andrew Vande Moere, Kristian Kloeckl and Carlo Ratti

2. Arc diagrams

3. Arc diagrams

4. Arc diagrams

5. Wattenberg, 2002
Steinweber and Koller, 2007
Heer et al, 2010
Kerr, 2003
Dörk et al, 2011
Wattenberg, 2006

6. Design goals
• Display node strength independent of edge
distribution
• Enable comparison of in-weight and out-
weight
• Emphasize total weight of a node

7. Spreading out imposts
Classic Arcs
Sankey Arcs

8. Algorithm
Classic arc diagram
Spread out arc bases
Reordered head and tail positions

9. Color coding for direction

10. Color coding for direction

11. Limitations
• Consumes more space
• Arc height does not always encode distance

12. Arc height does not always encode distance

13. Consumes more space

14. Consumes more space
Solution a)
Adapt node positioning
Equi-distant nodes
Equi-sized gaps

15. Consumes more space
Solution b)
Modify visual encoding

16. Scalability
Heer et al, 2010
Showing character relationships
of the novel Les Misérables.

17. Scalability
Reproduction
Removed color (encoded character groups).
Fixed edge width. Improved label display.

18. Sankey Arcs: Repositioned nodes

19. Sankey Arcs: Adjusted visual mapping

20. Case study: Public transit rides

21. Ridership Visualization

26. Sankey Arcs
• Display edge weights in path graph
• Have less visual obstruction by spreading out
arcs
• Allow comparing strength, and in- and out-
weights of nodes

27. Thank you. Questions?
Sankey Arcs, EuroVis 2012
Till Nagel, FH Potsdam, 06/2012
nagel@fh-potsdam.de – twitter: @tillnm