What is the symbolism of the bridges in the novel, Wildwood (Wildwood Chronicles)?

Each of the bridges represent the connections between the various worlds and people within the novel. The railroad bridge represents the connection between Wildwood and the Outside world of Portland. As far as anyone knows, it is the only way to cross the river to get near the Impassable Wilderness, but people from Portland never cross it, having nothing to do with the wild forest. Later, Prue learns about the Ghost Bridge which represents a connection to her magical past. Because her parents struck a deal on this unseen bridge, Prue is forever connected to Wildwood. The Gap Bridge represents the meeting point where the opposing forces in Wildwood meet. Alexandra and her coyotes live on one side of the deep ravine, and the bandits camp on the other. Just as the gap itself is wide, each group's purposes and plans for the land are very different. It is also on this bridge that the remaining bandits and the assembled army of North Wood meet and forge an alliance. The two groups are at odds, but for the benefit of all are willing to join together to fight a greater evil.