Assessing the Cartographic Visualization of Moving Objects

Abstract

Nowadays, there is a lot of interest in studying dynamic spatial phenomena. There are various dynamic phenomena in the world among which moving objects are worth exemplifying. Recently, moving objects are getting attention in database applications and in visualization. Moving objects are of two categories: individual moving objects and group moving objects. As visualization is important for various human activities like navigation, planning, monitoring, and academic accomplishments, the selection of the appropriate visualization method for a particular application is important. It is, however, not always known what ‘appropriate’ is in a particular context. This research is concerned with individual moving objects and their movement behavior. The research focused on visualization of the trajectory movement characteristics of these individual moving objects. The main goal of this research is to find the optimal representation for visualizing moving objects (more precisely: walking people). Four representations are considered in this research: the single static map, multiple static maps, animation, and the space-time cube. The study is conducted by considering four movement characteristics (or aspects of moving objects): speed change, returns, stops, and path of movement. The ability of users to perceive and understand these aspects from the four representation methods is studied. To achieve the goal, a user test is conducted using the questionnaire method (the users performing tasks). The visualizations were prepared on three levels of complexity - the complexity varying in the number of objects represented and the geometry of the trajectory along which they move (Level 1 with one object and simplest in complexity of geometry of the trajectory; Level 2 with two objects and more complex geometry of the trajectory; and Level 3 with three objects and most complex geometry of the trajectory). A prediction about suitability was made based on theory, cartographic knowledge, and common sense. The prediction shows that animation is better than the other methods for visualizing returns and speed change at all levels, and path at Level 2. In the other aspects and levels of complexity animation had equal suitability with the other methods. However, the prediction is not enough to make the selection of the best method for a particular use. Thus, user test is needed. The result of the suitability after test illustrates that users perceive and understand the movement characteristics better in an animation than in the other representations, at different levels of complexity. Animation is most suitable for stops at Level 1, for returns at Level 3, and for speed change at Level 1. In the rest, animation has equal suitability with one or more of the other methods, except for path at Level 2 where the space-time cube is most suitable. In the overall result, therefore, animation is found to be the optimal representation for moving objects (walking people). Key words: Change, Movement, Moving objects, Trajectory, Visualization, Single static map, Multiple static maps, Animation, Space-time cube