However, the links in mind maps are only associations, so mind maps have no definite structure.
To have a structure, a map should have some rules about nodes and links.
One way to make rules is to use visual metaphors,
for example the visual metaphor “down is more concrete”.
Another example of a visual metaphor: “down is subordinate”.
Cmaps are based on a visual metaphor:
“down is subordinate” and a rule
“links must have relation phrases (words that tell the relation between 2 nodes)”.