A vocabulary for a multiscale process description for fast transmission and continuous visualization of spatial data

With the increasing availability of small mobile computers there is also an increasing demand for visualizing spatial data on those devices. Prominent applications are location based services in general, and car and pedestrian navigation in particular. In order to be able to offer both detail and overview of a spatial situation, the devices have to provide flexible zooming in and out in real-time. The same demands arise from the increasing amounts of data available and accessible by web services through limited bandwidth channels. The presentation of spatial data sets in different zoom levels or resolutions is usually achieved using generalization operations. When larger scale steps have to be overcome, the shape of individual objects typically changes dramatically; also objects may disappear or merge with others to form new objects. As these steps typically are discrete in nature, this leads to visual 'popping effects' when going from one level of detail to the other. In this paper, we will present an approach to decompose generalization into simple geometric and topologic operations that allow describing the complete generalization chain to generate a multiscale object representation. The goal is to generate a representation without redundancy and to transmit only that information which is needed when scale changes occur. This representation scheme ultimately enables a continuous visualization, where the changes between the representations are visually indistinguishable. We identify elementary generalization operations and apply these concepts for polyline simplification, the generalization of building ground plans and for displacement.