Why should I use an SLD?

A web map server client provides data in a particular, read-only style. An SLD allows you to style the data in the way you want it to appear; in other words, you can decide on the appearance of map.

Since a web map server client is the visualization tool, it should have as much control as possible over the portrayal of the map, as it is the tool that the user interacts with to define the viewing parameters of the map.

The styled layer descriptor gives the web map server client some control over the visual appearance of the map, as well as the existing control over the combination of layers and viewing geometry. If a client is displaying layers from more than one web map server, then styled layer descriptor support from one or more of those servers allows the web map server client to resolve conflicts in styling of layers between servers. It is even possible for a client to pass off the control of the layer styling to the user, thus giving the user complete control
over the portrayal of the map.

With a styled layer descriptor, you can:

• Style data the way you want it to look without having it changed at the source or contacting the data
  provider;
• Share and use styled layer descriptor documents with others;
• Filter data that is returned from the web map server; and
• Turn data off and on at different scales.

Click on the links below for an example of an SLD.

OGC WMS GetMap URL with default styling:

1. This GetMap request URL for default styles returns a map as portrayed by the data provider.
   
   
2. This is the SLD document that styled the data.