OGC SLD/SE标准在专题制图方面的不足与扩展研究

网络地图制图目前已成为网络地理信息科学发展的重要方向,专题地图的网络制作尤为重要。OGC提出的SLD/SE标准是目前网络地图制图的标准和规范,但其描绘的地图质量不高,并且在描绘专题地图方面存在很多缺陷。随着网络地图制图的发展,一些SLD/SE标准外的网络地图样式语言逐渐兴起。与SLD/SE标准相比,新兴地图样式语言在制作专题地图方面存在优势。本研究从现有新兴地图样式语言中选择Mapbox GL和CartoCSS地图样式语言与SLD/SE标准进行对比,并总结当前标准的在专题制图方面的缺陷。研究发现,SLD/SE标准当中缺少设置分类方法的功能,同时还缺少用于准确表达未分类比例符号图的功能。针对这些缺陷,本文提出Classify和ProportionalSymbol扩展方案,将扩展后的SLD/SE标准应用于荷兰上艾瑟尔省的点、面矢量数据与使用当前标准描绘的地图进行对比应用研究,证明了本文提出的扩展在描绘专题地图方面更具优势。同时采用北京地区的点、面矢量数据并验证了扩展的普适性。SLD/SE标准目前仍处于不断改进的阶段,在未来的标准更新中,本文提出的2种扩展方案能在很大程度上简化制图者使用SLD/SE标准制图的工作量,并能改进SLD/SE标准不能描绘未分类的比例符号图的缺陷。

Research on the Deficiency and Extension of OGC SLD/SE Standard in Thematic Cartography

Nowadays, web cartography or web mapping has become an important direction for the development of web GIS. The production of thematic maps on the web is extremely important. The SLD/SE standard proposed by the OGC is currently the standard and specification of web mapping. However, SLD/SE standard is often at a fundamental level, which leads to poor quality of maps. With web cartography development, besides the SLD/SE standard, some new web styling languages are emerging. Compared with the SLD/SE standard, the emerging map styling languages have advantages in making thematic maps. This research selects Mapbox GL and CartoCSS from the existing emerging map styling languages for comparison with the SLD/SE standard, and then summarizes the defects of the SLD/SE standard in expressing thematic maps. The study found that the SLD/SE standard lacks the function of setting a classification method. Meanwhile, it also lacks the function of accurately expressing the unclassified proportional symbol map. Because of the shortcomings, this study proposed the extensions of Classify and ProportionalSymbol. Example data of Overijssel province in Netherlands were used to prove that the new extensions were feasible, while the verification data of Beijing were used to prove that the extensions were applicable to all vector data used to create thematic maps. The SLD/SE standard is still in the stage of continuous development. In future standardisation, the two extensions proposed in this research can greatly simplify the work of cartographers and improve the ability of current standard to express unclassified proportional symbol maps.