Dynamic cartographic network visualisation methods for limited viewports
1Gollenstede, A.; 2Weisensee, M.
1JADE UNIVERSITY OF APPLIED SCIENCES Email: firstname.lastname@example.org
2JADE UNIVERSITY OF APPLIED SCIENCES Email: email@example.com
The presentation of networks on maps helps users to explore, analyse and interpret relations between objects concerning a certain set of facts. Cartographic visualisation must consider several different types of networks with varying complexity. Typical scopes of application are schematic metro maps, street networks or power supply grids. Visualisation of more or less complex network maps on computer screens often becomes a demanding issue, because those screens are offering a rather limited viewport. Although screen size and resolution have increased during the last years, it is still a problem for the user to recognize all details and keep a good overview of the whole network at the same time. Nowadays presentations on computer screens often are realized by means of web based mapping solutions, which allow interactivity like panning and zooming or selecting and filtering the information shown on the map. Here, zooming helps to get detailed information of a certain part of the map. On the other hand, showing only subsections of the network makes it hard to get an overview about the whole set of facts and may lead to misinterpretations. Mobile devices, especially smartphones, are only offering an even smaller viewport. Thus, the task is to find an appropriate compromise between mobility and the ability to show as much information as needed or even possible. For the correct interpretation of the network or its subject it is often necessary to get information about qualities or quantities, which can be found outside of the current viewport. A first approach to a solution is to use a part of the viewport frame border to show graphical objects, which represent the actually invisible objects or the invisible network parts - herein called the "fringe". In the simplest case the fringe can be used to show where the next objects of the network are located and so it can support the user to pan into the right direction. But the fringe can also be used to give information about the number of objects or quantities outside the viewport. Therefore the graphical objects of the fringe can vary in size or colour or both. In the end all the traditional methods of cartography to visualise different kinds of quantities can be used here. Panning and zooming require a constant actualisation of the fringe. The fringe objects constantly move and change size and colour. Depending on the complexity of the network data a large amount of calculations need to be executed on the mobile client to animate the dynamic fringe. In addition to the fringe other types of animation can be used to support the user and to give an easy access to the network, e. g. showing animations of the edges, which are interconnecting the nodes of the network. If objects related to the network vary in time and place, a "live" animation of the network elements and the fringe is required. Representations like moving buses on a schematic public transportation map require a continuous update and animation of almost all elements on the screen. Then, the fringe can additionally contain information about the expected arrival of the next bus or the stations still to go for the passengers. In a first step different basic approaches are currently implemented and will be optimised for a proper cartographic presentation on mobile terminals. For these devices, especially the limited viewports are taken into account. As a second step the development and test of more sophisticated methods of visualisation and animation of networks on mobile devices will be tackled. Cartographic variables are to be analysed systematically in order to improve the functionality of the fringe as well as enhancing the comprehensibility. Furthermore, the project analyses, whether the used algorithms are suitable on mobile devices with regard to the still limited performance compared to desktop applications. Finally empirical test beds are planned to evaluate how users deal with those different ways of presentation.
dynamic cartography; network visualisation; limited viewport