Depiction of Multivariate Data Through Flow Maps

Flow maps are graphical representations that depict the movement of a geospatial phenomenon, e.g. migration and trade flows, from one location to another. These maps depict univariate spatial origin-destination datasets, with flows represented as lines and quantified by their width. One main feature of these maps is the aggregation of flows that share the same origin. Thus, visual clutter is reduced and the readability improved. This chapter describes a novel technique that extends flow maps to visualize multivariate geographical data. Instead of a univariate color scheme, we interpolate strategic color schemes to communicate multivariate quantitative information. Additionally, our approach crystallizes on augmenting flows with pie charts. To evaluate the relevance and impact of our approach, three case studies are presented.