This is a fusion of the Ancestor Diagram and Descendant Diagram for a All Diagrams have a root. This is the person from which the diagram “spreads out”; in the standard diagram preferences the root box is shown in a different colour from other boxes. person or couple.
It can be rendered in any direction, but the classic style is top down.
In 1st example below the root person is Ian Stephen MUNRO shown with the default white box background, and his sibling branches are included, but they can easily be excluded.
In 2nd example the root couple are Ian Stephen MUNRO & Charlotte CARRINGTON both with white box background, but no siblings.