Adjacency list to model relationships between relatively-positioned shapes?

I'm trying to model a composite object that consists of one or more shapes. For simplicity, I'll assume the shapes are all rectangles. A composite might look like this 开发者_运维百科(forgive my poor ASCII art):

+---+-------+---+
|   |   2   | 5 |
|   +-------+---+
| 1 |   3   |   |
|   +-------+ 6 |
|   |   4   |   |
+---+-------+---+

Wikipedia pointed me to graph theory, which I just barely remember from college, and it seems like an adjacency list would be a good way to model the relationships between all these shapes.

My question is, can I indicate left, right, top, and bottom relationships in an adjacency list? It isn't enough to say 1 is adjacent to 2; I need to say 1 is left of 2 (and 3 is above 4, etc.).

Sure. Where your normal adjacency list might look like:

vertex {
    neighbours: // list of neighbours
}

To include relative positions, each vertex could have an adjacency list for each direction:

vertex {
    left: ...
    right: ...
    up: ...
    down: ...
}

So:

3 {
    left: [1]
    right: [6]
    up: [2]
    down: [4]
}

and

1 {
    left: []
    right: [2,3,4]
    up: []
    down: []
}