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Practical use of GeoServer & SLD for WMS
Anders Söderman, GISassistANS AB
Hands on experience to learn methods for visualization enhancement in multi-source Web Mapping Services (WMS) using basic cartography rules. Web Mapping is the ultimate platform to discover, explore, share, and create content by combining distributed information and services. Combining different geodata sources may result in conflicting presentation styles and, consequently, in confusing maps.
The disadvantages can be reduced by using basic rules for web cartography. A webservice can be presented with a different cartography that is appropriate for the scope, e.g. crisis management or comprehensive planning. Many webmap services use solid, one pixel thick lines which often are horizontal, vertical or diagonal. If the distance between lines and choice of color is inappropriate, the interpretation is hampered significantly when different surfaces with similar patterning overlap.
One promising alternative is using map symbols in order to render polygons instead. Map icons are selected which can easily be associated with the surface theme, e.g., the Panda for the restricted areas due to environmental protection. Styles used in today's WMS services rarely adapt styles for different scales, which is often needed. PostgreSQL/PostGIS, GeoServer, QGIS and Inkscape are the tools used to produce styles using SLD. The Workshop includes for example:
- How to make the size of map symbols take into account the area of the polygon to be rendered, when using up to seven different scale intervals.
- How to customize map styles depending on user needs and thematic web map services.
- Labelling text from available attributes for lines and polygons.
- Saving SLDs in an HTML table using a PostgreSQL and PHP to quickly find information.
Using pictures to show the SLD together with a basemap gives an instant feel when looking for a style to copy and edit to make a new style. The participants should leave the workshop understanding that a combination of geodata should be able to interpret without having to examine the legend in detail.