GeoSciML-portrayal provides for web services that deliver polygons representing geologic unit outcrops categorized using identifiers from the CGI Simple Lithology vocabulary and the ICS stratigraphic time scale. The use of a shared map legend based on these categorization schemes provides first order lithologic and age harmonization between maps provided by different services. Map services from OneGeology Europe provide an example of this approach (see http://onegeologyeurope.brgm.fr/geoportal/viewer.jsp). The GeoSciML-portrayal schema provides an additional symbol-identification property to enable preservation of the legend units and portrayal from the original source map. This document is designed to facilitate the deployment and maintenance of geoscience information as interoperable, publicly available OGC web services in accordance with USGIN and OneGeology specifications.
see also tutorial at http://repository.usgin.org/sites/default/files/dlio/files/2012/u11/geosciml-portrayalcookbook0.7.pdf