Family trees

A family tree, or pedigree chart, is a chart representing family relationships in a conventional tree structure. The more detailed family trees used in medicine and social work are known as genograms.

Genealogical data can be represented in several formats, for example as a pedigree or ancestry chart. Family trees are often presented with the oldest generations at the top and the newer generations at the bottom. An ancestry chart, which is a tree showing the ancestors of an individual, will more closely resemble a tree in shape, being wider at the top than the bottom. In some ancestry charts, an individual appears on the left and his or her ancestors appear to the right. A descendancy chart, which depicts all the descendants of an individual will be narrowest at the top.

Family trees can have many themes. One might encompass all direct descendants of a single figure, or all known ancestors of a living person. Another might include all members of a particular surname (e.g. male-line descendants). Yet another approach is to construct a tree including all holders of a certain office, such as kings of Germany. This relies on dynastic marriage to hold together the links between dynasties.

The image of the tree probably originated with one in medieval art of the Tree of Jesse, used to illustrate the Genealogy of Christ in terms of a prophecy of Isaiah (Isaiah 11:1). Possibly the first non-Biblical use, and the first to show full family relationships rather than a purely patrilineal scheme, was that involving family trees of the classical gods in Boccaccio's Genealogia deorum gentilium ("On the Genealogy of the Gods of the Gentiles"), whose first version dates to 1360.

One technique is a "fan chart", which features a half circle chart with concentric rings: the person of interest is the inner circle, the second circle is divided in two (each side is one parent), the third circle is divided in four, and so forth. Fan charts depict paternal and maternal ancestors.

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