Towards Better WMS Maps Through the Use of the Styled Layer Descriptor and Cartographic Conflict Resolution for Linear Features

Abstract

The Open Geospatial Consortium (OGC) Web Map Service (WMS) and Styled Layer Descriptor (SLD) standards define a way of dynamically producing maps from vector data. However, this dynamic process often results in maps that are not easily readable when the underlying data are automatically represented at smaller scales than the original data were intended for. Fortunately, the SLD rules can be decoded, the symbolization rules translated into geometrical features, and cartographic conflicts detected and partially solved. The conflicting features can be identified based on the use of few basic geospatial analysis functions. After a solution that minimizes these conflicts emerges, new SLD rules are generated that attempt to visually solve the cartographic conflicts. The new SLD rules can then be applied on-demand by a cartographic proxy server that rewrites the incoming GetMap requests to use the new SLD rules. The process for improving the WMS cartographic output has several stages, grouped into preparatory steps (basic automatic generalization methods, rough scale-dependent SLD symbolization) and real-time processing steps (detection of cartographic conflicts, conflicts solution and generation of new SLD rules). The entire process of detecting and solving cartographic conflicts in the maps produced by WMS through the use of overriding SLD rules is described in detail. Furthermore, it is conceivable to transform the conflicting features into spatial objects containing methods for discovering appropriate SLD values that minimize conflicts. Such approaches can bring the performance of automatic detection and correction of cartographic conflicts above the threshold required for interactive visualization, thus, making the process of dynamically solving cartographic conflicts in WMS servers a viable solution.