VertexCoordinateRules is an option for GraphPlot and related functions which specifies rules for determining the coordinates at which vertices should be placed.
VertexCoordinateRules->{va->ra, vb->rb, ...} specifies explicit coordinates for vertices with names va, vb, ....
Vertices whose coordinates are not explicitly specified in the rules given by VertexCoordinateRules are automatically assigned coordinates by the graph layout procedure.
A setting vk->Automatic specifies that the vertex with name vk should be assigned coordinates automatically.
vk->{x, Automatic} defines an explicit x coordinate, but specifies that the y coordinate should be assigned automatically. vk->{Automatic, y} defines instead an explicit y coordinate.
EXAMPLES
Basic Examples 
Applications 
