Adaptive zooming in web cartography

Beyond any doubt much of the current web mapping and web GIS applications lack cartographic quality. The reasons aren't only the technical limitations related to Internet delivery, but also the neglect of one of the main cartographic principles of digital mapping, namely adaptive zooming. Adaptive zooming describes the adjustment of a map, its contents and the symbolization to target scale in consequence of a zooming operation. The approach described in this paper proposes the combination of two commonly known concepts: on the one hand levels of detail (LoD) for those object classes, that require high computational cost for the automated generalization process (e.g. buildings, road network); on the other hand an on-the-fly generalization for those object classes which can be generalized by less complex methods and algorithms (e.g. rivers, lakes). Realizing such interactive and dynamic concept for web mapping requires the use of vector based visualization tools. The data format best meeting the criteria is the W3C standard Scalable Vector Graphics (SVG). Thus, it has been used to implement the presented ideas in a prototype application for topographic web mapping based on the landscape model VECTOR25 of the Swiss Federal Office of Topography.