Specifies where to place the node on the map. Coordinates are in pixel units, with the origin at the top-left of the map.
Optionally, you can also specify another node that the coordinates are relative to. This allows you to have 'sub-nodes' that follow a master node around as you alter the map. Relative nodes can be relative to other relative nodes, as long as the node at the end of the chain is not relatively positioned!