Using Graph Layout to Visualize Train Interconnection Data

Abstract

We are concerned with the problem of visualizing interconnections in railroad systems. The real-world systems we have to deal with contain connections of thousands of trains. To visualize such a system from a given set of time tables a so-called train graph is used. It contains a vertex for each station met by any train, and one edge between every pair of vertices connected by some train running from one station to the other without halting in between.In visualizations of train graphs, positions of vertices are predetermined, since each station has a given geographical location. If all edges are represented by straight-lines, the result is visual clutter with many overlaps and small angles between pairs of lines. We here present a non-uniform approach using different representations for edges of distinct meaning in the exploration of the data. Only edges of certain type are represented by straight-lines, whereas so-called transitive edges are rendered using Bezier curves. The layout problem then consists of placing control points for these curves. We transform it into a graph layout problem and exploit the generality of random field layout models for its solution.