Sequential displacement and grouping of point symbols in a mobile context
Janne Kovanen, L. Tiina Sarjakoski · Journal of Location Based Services · 2013
The need to improve the methods of displaying point symbols on mobile maps is becoming more and more crucial. As the number of symbols on maps increases and the maps allow intelligent zooming, the overlapping of symbols needs to be resolved by automated cartographic generalisation methods, such as aggregation or displacement. This paper introduces an algorithm for grouping overlapping point symbols in a sequential and cartographically pleasing fashion. The method displaces the point symbols adjacently based on the changing scale. In addition, the algorithm implements the aggregation operator for similar symbols lying nearby and, in the grouping process, it takes into account the symbol hierarchy resulting from the context. Before displacement, the objects are filtered based on the level of detail and ordered according to their relevance and coordinate values. When the point symbols do not fit onto the map view, another generalisation method, such as point symbol clustering, is applied to the symbols. To empirically validate the concept, the method was implemented on a map application run on a mobile smartphone and a tablet computer. The application supports multiple zooming levels and requires an efficient client-side method for displacement. The running performances for the algorithm are also given in this paper.