The distance between nodes in a tree graph in the longitudinal direction. The longitudinal direction means the direction that the chart flows - in a horizontal chart the distance is horizontal, in an inverted chart (vertical), the distance is vertical.
If a number is given, it denotes pixels. If a percentage string is given,
the distance is a percentage of the rendered node width. A nodeDistance
of 100% will render equal widths for the nodes and the gaps between
them.
This option applies only when the nodeWidth option is auto, making
the node width respond to the number of columns.