Styled Layer Descriptor
From GISWiki
The Styled Layer Descriptor (SLD) is an encoding for how the Web Map Server (WMS 1.0 & 1.1) specification can be extended to allow user-defined symbolization of feature data.
Editor
AtlasStyler is a visual editor for SLD files. It allows to create advanced stylings for given vector data: e.g. statistical classification of quantities, classification by unique values, and labeling. The LGPL Java application is based on Geotools 2.4 and Swing. It can be used online from the webpage.
