DIAGRAM MARKUP LANGUAGE - A NEW MODEL FOR SYMBOLIZATION IN INTERNET MAPS
O. Schnabel, L. Hurni
ETH Zurich, Institute of Cartography, Zurich, Switzerland
With currently available mapping and GIS software it is still hard to efficiently and easily create diagrams for internet maps. In nearly all programs complex symbolization such as bar or pie charts is just hardcoded in symbol libraries or with scripting languages. A more flexible approach is the use of description languages like Styled Layer Descriptor (SLD) to model map symbols. But SLD can only create proportional symbols and lacks the possibility of diagram creation in internet maps.
To provide the advantages of a cartographic description language, a XML based Diagram Markup Language (DiaML) was developed to describe the symbolization of statistical data. In contrary to current approaches no scripting or programming is necessary to adapt the symbol appearance to the user's need. Especially the portrayal of multiple data values can be easily modeled with DiaML. As potential visualizations, proportional symbols, repeated symbols and charts (e.g. pie charts, bar charts, wing charts, dot scatter charts) are at the users disposal.
While current mapping software select only few of the large number of symbolizations, DiaML uses a new and innovative construction model to integrate as many symbols and diagram types as possible in the cartographic description. In DiaML, the symbolization is separated in simple symbols visualizing only one data value and diagrams visualizing multiple data values. Both consist of cartographic primitives. The ten integrated primitives are: point, polyline, curve, ellipse, circle, pie sector, ring, ring sector, rectangle (bar), and regular polygon. These primitives can be scaled in one or two directions depending on the data values. Therefore, the minimum and maximum data values as well as the minimum dimensions and the ratio between the map area and the symbol area are necessary to calculate the symbol scale. Furthermore, the scaled primitives can be ordered following few arrangement principles. Simple symbols use the arrangement principles "centered" (for proportional symbols) and "grid" (for repeated symbols). The cartographic primitives for diagrams will be arranged "polar", "linear", "rectangular", or "triangular". Additionally, map symbol properties such as transformation parameters (e.g. rotations and translations), guides and interactive labels as well as graphical properties for each primitive (styles) were integrated in the new cartographic model. To increase the reusability of the DiaML descriptions, the primitive and style definitions were separated from symbol description. Therefore, the description is much shorter than a SLD description, since the styles and primitives need only be defined once.
The DiaML description language was applied in a web application called "Map Symbol Brewer" to demonstrate the applicability of the new symbolization model. Here, the DiaML description can be read and converted to a visualization. The application can be regarded as symbolization service. Generally, the flexibility, readability and mainly usability of cartographic description languages such as DiaML increases the potential of the cartographic visualization.