This may seem like a newbie question, but I've been trying to answer this on my own and not making any progress. I understand the concept of the Constellation Plot intuitively as showing the membership in clusters as they're built up from the dendrogram. JMP puts labels on the axes (-200 to +200 in my case), which begs the question. The explanation that "Longer lines represent greater distances between clusters" doesn't really explain the two dimensions.
The x/y positions and axes are only present so you can do normal JMP graph operations, like zooming or adding customizations. The plot is mainly just showing the structure of the tree (e.g., balanced or not). The nodes themselves are positioned to avoid collisions.