Creating Thematic Maps with OGC Standards Through the Web
Marta Duarte Teixeira, Rafael de Melo Cuba, and Gerson Mizuta Weiss - CPqD TELECOM & IT SOLUTIONS
This paper presents a WEB based component and some extensions proposed to OGC standards in order to build a configuration tool for thematic maps. Thematic maps make it possible to perform graphical evaluations. The visualization of thematic maps is a very useful and important feature of a GIS. A thematic map can show, by the use of colors, patterns, graphics or charts, the distribution of a single or multiple phenomenons over the Earth’s surface. The proposed component uses only OGC standards to communicate with other components in a GIS solution. The available layers, features and styles are recovered using a WMS server. Additionally, feature type properties and the data needed to build the classification attributes are obtained by the use of a WFS server. All the resulting styles are described in SLD. The design of this component requires some extensions in OGC standards. The SLD specification does not allow the representation of bar graphs and pie charts, usually presented in thematic maps. One can use SLD rules to define themes by a single value or a range value, but it is not the appropriate way to build thematic maps. In this context, we propose some extensions to the SLD specification. New interfaces to the WFS are also proposed to get histograms data, made of values and frequencies, about feature types related in a thematic classification. The results can be used as a proposal of extension to some OGC standards like SLD and WFS and can improve the interoperability among GIS.