Spider diagram is used to visually organize information, not in a horizontal or vertical way but in a manner that all the information are organized surrounding a single major concept. First order ideas are derived directly from the central concept, and second order ideas are connected to the first order ideas, etc. Other ideas keep branching out from the higher hierarchical ideas. For details see the wiki page of Mind map.
I have summarized EPI theories into spider diagrams to prepare for the USC Epi PhD screening exam. These diagrams helped me understand and memorize Epi theories better.
For example, below is a spider diagram for Noncomparability: