Polyline Morphing for Animated Schematic Maps

Abstract Thematic maps allow for the visual analysis of spatial data. When comparing two map states, preserving the mental map of a user facilitates the comparison. One way to achieve this is to use animated transitions between the states. This work presents an algorithm for computing such animations, called morphs, between schematized map objects, a technique particularly pertinent in urban mobility scenarios where schematic maps improve map legibility. In schematic maps, abstraction is used to reduce the visual complexity while still conveying information on a selected phenomenon. Our method ensures that the morph has four favorable properties: (1) it is self-intersection-free, (2) it maintains the schematization of the input features, (3) it is self-contained, and (4) every segment moves at its own constant velocity. We present an efficient algorithm to compute vertex traces and the timing of the morph. We evaluate our approach on isochrones visualizing travel times and on different layouts of schematic transit networks. The results show that the additional constraints we induce on the morphing only have a minor influence on the optimization target while they reduce the complexity of the animation.