The Thesaurus for Graphic Materials I: Subject Terms (TGM I) provides a substantial body of terms for subject indexing of pictorial materials, particularly the large general collections of historical images which are found in many libraries, historical societies, archives, and museums. Developed to support the cataloging and retrieval needs of the Library of Congress Prints and Photographs Division, TGM I is offered to other institutions in the hope that it will fill similar needs and will promote standardization in image cataloging. TGM I is primarily designed for automated cataloging and indexing systems and is authorized for use in MARC (Machine-Readable Cataloging) records. The vocabulary can also be used, however, in manual indexing systems, whether card catalogs or vertical files of pictures.
TGM I may be used to index subjects represented in a variety of still image media and formats, including prints, photographs, drawings, posters, architectural drawings, cartoons, and pictorial ephemera. The thesaurus provides a controlled vocabulary for describing a broad range of subjects depicted in such materials, including activities, objects, types of people, events, and places. TGM I includes subject categories only. Thus, proper noun names of people, organizations, events, and geographic places are excluded.  Art historical and iconographical concepts are not included either, but TGM I does supply terms for abstract ideas represented in certain types of images, such as allegorical prints and editorial cartoons.
TGM I is designed as a tool both for those who create catalog records and for those who search for them. Entry vocabulary and scope notes are designed to serve a dual purpose: assisting indexers in selecting terms for indexing and helping researchers find appropriate terms with which to search for pictures. At present, TGM I contains 5,504 authorized ("postable") terms, and 4,324 cross-reference ("non-postable") terms, giving it a very high ratio of entry vocabulary and increasing the ease with which searchers can translate their own terminology into the language of TGM I.
TGM I adheres to the American National Standards Institute (ANSI) guidelines for thesaurus construction.  In developing TGM I, emphasis has been placed on providing easily readable notations, logical hierarchical relationships, terms structured in natural language order, clearly distinguishable public notes and cataloger's notes, and modern American spelling conventions.
Although the primary purpose of TGM I is to serve as a source of terminology for topics represented in graphic materials, it also offers indexing guidelines. Indexers trained to analyze textual materials may not know how basic indexing practices can be applied to pictorial indexing. It is hoped that the guidelines presented in this introduction will help in this regard and lead to consistent application of TGM I.