Consistent use of chronological subdivisions is an aid to organizing images or descriptions of images of a particular subject in an ascending or descending date order, resulting in a file arrangement that presents the evolution of the subject over time.
All TGM I terms may be subdivided chronologically. P&P has generally based the chronological subdivision on the year of execution, i.e., the year that the material being cataloged was created. When an image portrays a subject whose chronological orientation is significantly different from the year in which the original image was made (for instance, a lithograph made in 1924 depicting a scene from the American Revolution), it may be desirable to base the subdivision on the year of depiction.
Since all terms may be subdivided chronologically, this facet is not enumerated under each term in the thesaurus. Each institution must determine its own scheme for chronological subdivision. In order to provide a predictable set of dates in systems which do not feature truncation or range-searching, P&P has adopted a practice of subdividing by the decade(s) span that encompasses the year(s) of execution/depiction.
Example: Photograph taken of lion hunting in Africa in 1933. [Thesaurus] Lion hunting [Indexing string] Lion hunting--Africa--1930-1940 Example: Engraving made between 1822 and 1865 that shows a theater in Atlanta. [Thesaurus] Theaters --[country or state]--[city] [Indexing string] Theaters--Georgia--Atlanta--1820-1870 Example: Cartoon drawn in 1955 showing a Confederate general during the Civil War. [Thesaurus] Generals --[nationality]--[country or state]--[city] [Indexing string] Generals--Confederate--1860-1870
MARC coding: Chronological subdivisions are assigned subfield code "y."