  Showing flows of people and resources between multiple geographic locations
is a challenging visualisation problem. We conducted two quantitative user
studies to evaluate different visual representations for such dense
many-to-many flows. In our first study we compared a bundled node-link flow map
representation and OD Maps [37] with a new visualisation we call MapTrix. Like
OD Maps, MapTrix overcomes the clutter associated with a traditional flow map
while providing geographic embedding that is missing in standard OD matrix
representations. We found that OD Maps and MapTrix had similar performance
while bundled node-link flow map representations did not scale at all well. Our
second study compared participant performance with OD Maps and MapTrix on
larger data sets. Again performance was remarkably similar.
