Hierarchical graphs are graphs in which hierarchical relationships exist between the members and hence the graph can be visualized with multiple levels.

A simple example of a hierarchical graph is a family tree. In a family tree, each member is depicted as a node; a relationship (or an edge) exists between two nodes if they are spouses or if they have parent-child relationship between them. This tree can be represented as a hierarchical graph visualized as a vertical-levelled graph with members at each level belonging to the same generation.

A convex hull for a set of points (in our case, nodes of the graph), in simplistic terms, is the minimal closed structure that would enclose all the points inside it. It can be visualized as an enclosure obtained when a rubber band is stretched around the set of points in consideration.