Adding to your collection
Looking at the catalogue
Sorting is the means by which we decide the order in which to
In the traditional stamp catalog, the catalog editors assign catalog numbers to each stamp, using rules that may or may not be known to anybody else, then have the catalog list all the stamps in order. While some of the rules are obvious (lower face values before higher, earlier issues before later ones), other decisions are mystifying. In some cases the choice must be arbitrary - when the same stamp is issued in several different colors for the same denomination, there is no "standard" order in which to list colors.
StampData establishes a single formula for sorting. In addition to the usual tests of date etc, issues and individual stamps have sort positions, which are numbers that represent relative position among similar types.
Issue sort positions are needed when there are a number of issues that share the same base date. This typically happens in one of two ways:
Stamp sort positions are necessary within issues that consist of stamps with several different designs, but all with the same face value.
(At some point this will likely be changed to include secondary denomination, as for semipostals, and the denomination of the base stamp of an overprinted type.)