Genealogical numbering systems

Several genealogical numbering systems have been widely adopted for presenting family trees and pedigree charts in text format. Among the most popular numbering systems are: Ahnentafel (Sosa-Stradonitz Method), and the Register, NGSQ, Henry, d'Aboville, Meurgey de Tupigny, and de Villiers/Pama Systems.

Ahnentafel, also known as the Eytzinger Method, Sosa Method, and Sosa-Stradonitz Method, allows for the numbering of ancestors beginning with a descendant. This system allows one to derive an ancestor's number without compiling the list and allows one to derive an ancestor's relationship based on their number.

The number of a person's father is the double of their own number, and the number of a person's mother is the double of their own, plus one. For instance, if the number of John Smith is 10, his father is 20, and his mother is 21.

The first 15 numbers, identifying individuals in 4 generations, are as follows:

In order to readily have the generation stated for a certain person, the ahnentafel numbering may be preceded by the generation, hence (with more readable alternative):

This method's usefulness comes readily into view when applied further back in the generations, e.g., 08-146, is a male preceding the subject by 7 (8-1) generations. This ancestor was the father of a woman (146/2=73) (in the genealogy line of the subject), that was the mother of a man (73/2=36(.5)), further down the line the father of a man (36/2=18), father of a woman (18/2=9), mother of a man (9/2=4(.5)), father of the subject's father (4/2=2). Hence, 08-146, is the subject's father's father's mother's father's father's mother's father.

atree or Binary Ahnentafel method uses the same numbering of nodes in the binary ancestors tree as Ahnentafel method, but uses binary numbers instead. For a female in the root the correspondence between binary and atree numbering is straightforward, but for male in the root - the first digit is 1 (i.e. M anyway) - to avoid trimming 0s. The advantage of atree system is easier understanding of the genealogical path (as a path from the root) and binary numbering system is natural for the binary tree.

The first 15 numbers in 4 generations in atree system (note that "M" and "F" represent "male [ancestor]" and "female [ancestor]" respectively, as opposed to "mother" and "father"):

Explanation of the correspondence between atree IDs and Ahnentafel decimal IDs:

Genealogical writers sometimes choose to present ancestral lines by carrying back individuals with their spouses or single families generation by generation. The siblings of the individual or individuals studied may or may not be named for each family. This method is most popular in simplified single surname studies, however, allied surnames of major family branches may be carried back as well. In general, numbers are assigned only to the primary individual studied in each generation.

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