One of the reasons for using mind maps is to help with making notes of other peoples work - such as books but also articles, lectures, presentations , TV shows and podcasts. In other words any situation where you are hoping to absorb and understand somebody else’s ideas.
In many cases what you may try to do is to write as many notes as you possibly can to ensure that you don’t miss out anything important. However this approach can be exhausting as you will be writing all the time and you might find yourself so focused on what you are writing that you are not really paying attention or thinking about what is being said.
Not everything in the book or lecture will be of equal weight or importance. There is a great deal of redundancy in our use of language. When making notes, you should try to write down only key words and key concepts. These are the ideas that are absolutely essential to the meaning. Try it with this article. Print it off. Go through it and see how many words you can cross out while still retaining the underlying meaning. Whatever is left should be the key words and key ideas.