Probably the most significant change in TGM I has been in the addition of 1,937 postable and 1,755 non-postable terms. Additions and changes to the vocabulary are a direct outgrowth of the cataloging that has been going on in P&P and a few contributing organizations over the past seven years. The cataloging of groups of photographs, including many relating to Native Americans, and a program to catalog single items for which orders for reproduction have been received--ranging from Currier & Ives prints and Civil War drawings and photographs to 20th century fine prints and World War II posters--have resulted in many new terms. Other recent projects have focused on cataloging groups of architectural drawings and architectural photographs. These cataloging ventures have resulted in the addition of more specific vocabulary (Houses has been added as a narrower term to Dwellings, for instance). Coinciding as they did with the publication of the AAT, such projects have also spurred a re-examination of the terms used for buildings and sites and of the relationships that exist among them. Appropriately enough, this has resulted in a new structure, founded on the concept of Facilities, a broader concept than Buildings. This new structure attempts to incorporate many terms that were previously "orphans" (i.e., they had no broader term), while remaining flexible enough to be used in situations that show combinations of site, structure, and activities characteristic of a particular type of facility. A corresponding structure for Architectural & site components has also been developed.
Changes in terminology, while inevitable, can be time-consuming to implement in indexing systems or, if not fully implemented, can place burdens on the users who must then search under old and new terms. While some term changes have been necessary, particularly in the context of the work on Facilities, an attempt has been made to keep major changes to a minimum and to alert users of TGM I to changes that have occurred by recording history notes under changed terms.
The lists of topical subdivisions used by P&P have been restructured and expanded since the first edition; they include, for the first time, subdivisions used with names of corporate bodies and names of wars (see Appendices A through D). Other differences from the first edition include greater allowance for geographic and nationality subdivision (see Section III for a discussion of subdivision practice). Public and cataloger's notes that were found to be too local or limited in their application have been eliminated or altered. Cataloging examples have been added to illustrate some of the indexing principles and practices employed by P&P catalogers.