How a family tree works and how to read one

A family tree works by giving each generation its own row

A family tree is a chart of who descends from whom. The oldest generation stands in the top row, their children stand in the row below, and the grandchildren stand below them. Everything else on the chart follows from that one rule, so a reader who finds the rows can read any tree.

The Alder tree on this page holds twelve fictional people. Walter and Edith Alder and Hugh and Marian Whitlock are the grandparents. Their children Ruth, Thomas and Clara stand in the second row with Paul Benton, who married Ruth. The four grandchildren, Isla, Max, Nora and Eli, stand in the third row.

Read down the chart for descent and up the chart for ancestry

Direction is the first thing to settle. Reading down from Walter and Edith answers who their descendants are. Reading up from Nora answers who her ancestors are, which is the question most people bring to a tree. Nora carries a double outline on this chart because she is the person the tree starts from.

Within a row, the children of one couple are drawn in order of birth, with the oldest on the left. Isla, born in 2001, stands to the left of Max, born in 2004. Some trees run the other way and put the starting person at the bottom or at the left edge, with the ancestors spreading out from there. The rule of one generation to a row or a column still holds.

Two kinds of line carry most of the meaning

A horizontal line between two people joins a couple. A vertical line that drops from the couple line leads to their children, and a bar across the top of several children marks them as brothers and sisters. On the Alder tree the line between Thomas and Clara carries the year they married, 2002, and the line below it splits to reach Nora and Eli.

The small marks around a person add the facts. The table lists every mark on the Alder tree.

Count generations by rows and not by ages

A generation is one step from parent to child. Grandparents, parents and children make three generations, however many people stand in each row. Age is a poor guide, because in a large family an uncle can be younger than his niece. On the Alder tree Paul was born in 1970 and Clara in 1977, and both belong to the second generation because each married a child of the first.

The people directly above and below you form your direct line. For Nora that line runs through Thomas to Walter and Edith, and through Clara to Hugh and Marian. Genealogists call these relatives lineal. Every person has two parents, four grandparents and eight great-grandparents, so the direct line doubles with each row you climb.

A collateral branch starts from a brother or sister of an ancestor

Relatives who share an ancestor with you without being in your direct line are collateral. They sit on branches that leave the direct line at a brother or a sister. On the Alder tree the branch starts at Ruth, the sister of Thomas. Ruth married Paul Benton, and their children Isla and Max carry the Benton name.

To name a collateral relative, climb from yourself to the couple you share and come down the other side. Nora climbs two rows to Walter and Edith and comes down two rows to Isla, so the two are first cousins. Ruth is one row below the shared couple, so she is the aunt of Nora. The guide to family tree relationship terms places nieces, in-laws and cousins once removed on one chart.

Read any family tree in five steps

The same order works on a printed chart, a school project and a tree in a genealogy program.

A genogram keeps the same rows and adds more about the people

A family tree records names, dates and descent. A genogram uses the same rows and lines and adds the kind of each relationship, health conditions and who lives together, which is why clinicians and students draw one. The comparison of a genogram and a family tree sets the two side by side and says when to choose each.

The chart on this page was drawn in Genogram Builder as a plain family tree, with no conditions and no relationship lines. To draw your own, follow Start a new genogram, then Add a partner and Add a child for each couple. Mark the index person gives the starting person the double outline.