Cluster diagrams are another way to mind map by starting with the keywords first.
Sometimes the term cluster diagrams is just used to mean mind maps. Other times the term means to start by randomly writing down all the keyword ideas on a piece of paper, flip chart, or white board.
When it appears as if there are plenty of keyword ideas or when it seems as if the flow is slowing down, you take a different color and start drawing lines (like a lasso) around the ideas that seem to fit together. Then for each cluster of keywords you come up with a single keyword or short phrase that could be a heading for that group. Finally, you rearrange the sets of keywords into the mind map form and continue to brainstorm.
Working your keyword diagram by brainstorming randomly first can be a freer way of thinking about the topic or question as you first get started. For some groups or individuals this seems like a more natural brainstorming method.
Some school districts teach the clustering method. It is important that schools teach children some form of mind mapping or clustering since it improves a child's ability to organize their learning and to study more efficiently for tests.
My recommendation is that you try cluster diagrams sometimes and other times mind map out from central concept or topic. You can decide if one works better for you or works better in some situations. It is also an excellent way to vary the methods to keep your brainstorming sessions fresh and interesting, and most of all productive.