3D mind maps

I can't understand how the topic cones are related

"Does the size represent how many documents are inside a topic? How do I know what is a child of what? How does a 3D mindmap relate to a 2D one?"

We have a page devoted to this topic. You can click this link to open an illustrated page explaining Topicscape's structure (what the cones mean, their positions and their relative sizes) in another browser window.

Here is an article about mind mapping and concept mapping in 3D.