Style Layer Descriptor

The Style Layer Descriptor file format is an XML document defined by the Open Geospatial Consortium. Style Layer Descriptor documents defines how Features are rendered on to the screen.

You can use your own Style Layer Descriptor documents in several ways:

Select the XML page of the Style Editor Dialog and directly modify what is being used directly
Any sld file associated with a shapefile will be picked up and used
You can import and export SLD files from the Style Editor Dialog
you can drop an SLD file directly onto a Layer

Style Editor Dialog
Styled Layer Descriptor (OGC Specification)
Symbology Encoding (OGC Specification)
SLD Examples (from MassGIS)
SLD Intro Tutorial (from GeoServer)
SLD Samples (from GeoServer)