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1.3.6. Styled Layer Descriptor

"The Styled Layer Descriptor (SLD) is a companion specification to the web map server (WMS) interface specification." (Geoconnections.org)

The OpenGIS Styled Layer Descriptor (SLD) Implementation Specification is an encoding that extends the Web Map Service specification to allow user-defined symbolization of feature data. It allows users (or other systems) to determine which features or layers are rendered with which colours or symbols. (OGC)
An example: if a water-bodies layer on a WMS server portrays the water features with the default colour of black, the adding SLD support on the server allows the WMS client to specify that it wants the water features returned as blue. (Geoconnections.org)

The importance of visual portrayal of geographic data cannot be overemphasised. It is needed for geospatial consumers (either humans or machines) to control the visual portrayal of the data with which they work. The current OpenGIS Web Map Service (WMS) specification supports the ability for an information provider to specify very basic styling options by advertising a preset collection of visual portrayals for each available data set. However, while a WMS currently (in 2006) can provide the client with a choice of style options, the WMS can only tell the client the name of each style. It cannot tell the client what portrayal will look like on the map. More importantly, the client has no way of defining its own styling rules. The ability for a human or machine client to define these rules requires a styling language that the client and server can both understand. This language is called the Styled Layer Descriptor (SLD). (OGC)
The SLD gives the WMS client some control over the visual appearance of the map, as well as the existing control over the combination of layers and viewing geometry. (Geoconnections.org)

Following you see a request result of a web map service without SLD (above) and with SLD (below).

Web Map Service without SLDWeb Map Service without SLD (UMN MapServer)Web Map Service with SLDWeb Map Service with SLD (UMN MapServer)

If you are interested in how to use the Styled Layer Descriptor consult the following literature (please read first the chapters Web Map Service and Web Feature Service):



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