Dynamic Visualisation Of Journey-To-Work Flows Using Map Morphing

Abstract

Visualisation of spatial interaction flows is a challenging task. Flow maps are quickly cluttered and difficult to read, even with a relatively small number of flows. This paper introduces a novel approach where the flow map is embedded in a cartogram-like map morphing projection. The classic areal cartogram creation step is divided in two tasks. In a first step, a new cartogram projection is computed, and in a second step, the spatial interaction flows are projected into this new space. The population density or the flow density can be used for creating the cartogram projection. The big agglomerations, where the most interaction flows occur, are visually increased in size, and the clutter reduced. This technique is shown in a dynamic, interactive application for roughly 184’000 journey-to-work movements for nearly 3000 communes in Switzerland. The emerging technology of WebGL allows for mapping such high numbers of flows inside an interactive Web-based application. The interactivity helps the user in identifying locations and flows in the cartogram display.