A vertex map carries vertexes of one complex to vertexes of another.
When modeling a robot system as a graph, links are modeled as vertexes and joints are modeled as edges.
The vertexes of meshes are the position of passive particles.
Vertices (or vertexes as they are referred to internally) are then joined to form lines, known as linedefs.
In essence, every edge is just an internal node of a tree or directed acyclic graph, and vertexes are the leaf nodes.
Objects may be composed of primitives such as spheres, or more complex shapes made by extruding polygons along the z axis and adjusting the vertexes.
The geometrical meaning of this manipulation is the manipulation of the convex hull defined by the vertexes.
A polygon is an area formed from at least three vertexes (a triangle).
