U.S. Geological Survey Photographic Library
The Vocabulary 
Currently, there are no vocabulary controls and the librarian I interviewed mentioned that “moving to a standardized metadata scheme implies the use of thesauri and similar controlled structures.” I went through with the librarian asking about the decision to create the vocabulary or if there is a trigger for creating a term, but there isn’t for the website. As unstandard as the design is, the collection does have an extensive thesaurus: The thesaurus is a contolled vocabulary list of terms in a hierarchy that for a given concept is given a preference referred to as the descriptor. Lead-in terms or non-preferred terms are not always a synonym of the preferred term, and these terms are generic relationships. This collection specifically utilizes the USGS Thesaurus, which is for science topics. The USGS Thesaurus Working Group is composed of specialists in library and information sciences, communications, the natural sciences, scientific software development, and data management. Its purpose is to create and maintain controlled vocabularies, use those vocabularies to create catalogs and indexes, and develop methodology that will help people find and understand online USGS information resources. The group is associated with the USGS home page design team and coordinates its work with other project tasks as appropriate.
Standards conformance The USGS Thesaurus is the principal controlled vocabulary supporting Science Topics. It is designed as a formal thesaurus conforming to ANSI/NISO Z39.19, with rigid adherence to the hierarchical (BT, NT) term relationships, generic non-hierarchical (RT) relationships, and lead-in term relationships linking non-preferred terms to descriptors either singly (UF) or in a compound USE-WITH relationship. The thesaurus is faceted, meaning its top terms delineate general aspects of information resources.
Usage  Each information resource in the Science Topics catalog is categorized using several index terms. Consequently a document will be listed under each category for which it would be considered a relevant resource. Approximately 1200 web resources are listed in the catalog.
Top Terms Sciences  Methods  Topics  Product types  Time periods  USGS
USGS Thesaurus