There are several thinking tools I use, but I don't often think about the tools, their advantages, and their limitations. When I did a search on Mind Maps AND Affinity Diagrams, not much showed up that compared the two, so I thought I would puts some thoughts down and share them to see what other people think.
My most common tools are linear notes, mind maps, and affinity diagrams. In all three cases, creating an artifact aids thinking by feeding back to me a prior thought. I experience the same dynamic for other creative processes. When I create software, I model architecture with UML and code. Both speak back to me and generate more ideas. If I am building a financial model, I can run scenarios and let the model show me the results.
These tools have the greatest advantages when two conditions are present: complexity and groups of people. Software is complex. Just try to write software in your head, then write it down after you are done. The mind is amazing, but it can't keep very much code in it. With multiple people, an artifact works like shared memory. Every idea feeds back to every mind to generate more ideas.
IDEO works with these dynamics. A group of people have a problem, and they prototype solutions as a group. The prototype is the artifact. When complexity and multiple people are combined with a flexible medium, there is a third dynamic. Not only do ideas go into the artifact, and the artifact speaks back, people discuss the artifact with each other. This cross-pollination process tests concepts, compares interpretations, and generates ideas.
Let's look at the three tools individually, compare them, and consider how they influence thinking.
Notes are as old as the hills. In the old days of paper and pencil, the only place you can write is at the bottom or between the lines. With computers, you can write anywhere. Nonetheless, information is mostly one dimensional except to the extent that you use bullets and tabs. Notes are easy because you can record a stream of consciousness, record a lecture, or just dump your short term memory before you forget something. Linear notes match how you read a book or article like this one. If you are writing a book, even through the book has structure, you are serializing the information. When you read, you are processing information serially, much like listening. When you write, you communicate thoughts, much like speaking.
Linear notes match our input-output devices more than our thought patterns.
Mind Maps and Affinity Diagrams
These diagrams present information in a more parallel fashion. they are inherently multi-dimensional. Information is connected in tree form. The paper layout is two dimensional, and there is hierarchy. If nodes have sentences, these diagrams contain linear notes within them. If nodes have single nodes, they are more parallel in nature.
A mind map starts with a central image. Then you draw your first branches. These are described by Tony Buzan as Basic Ordering Ideas. Branches are then added to branches. Child branches are associations of ideas. Buzan emphasizes that branches get smaller as you get away from the central image and each branch has one word. By avoiding sentences on a single branch, you can add ideas at the granularity of a single concept.
This mind map is a combination of single words and sentences.
Affinity diagrams are normally built with sticky notes. The process begins with a collection of notes and affinities are discovered by looking and grouping. Once groups are formed, higher level groups are formed until you have a small number of groups or one group. The end result is a hierarchy. Individual notes are almost always sentences, so there is always a linear aspect of an affinity diagram. It reminds me of a concentration game. You flip two cards and try to match them. You have to remember where cards are so when you flip one card, you remember where the match is. It is a pattern matching game.
This is a generic example from mindtools.com. Random ideas are organized into themes. (Source Mind Tools)
Even though the form of the result appears similar, the processes involved could not be more different. Mind mapping tends to be a very top down process. You start with a central idea, then put down Basic Ordering Ideas. (Note the term "Ordering") From these branches come more. If you work from the center out, the mind map can develop very analytically from whole to part. Buzan claims that the mind map breaks the left brained linear thinking process and aids whole brain thinking. I believe this depends completely on the process, not the representation. Nonetheless, because a mind map begins with Basic Ordering Ideas and unfolds by triggering ideas in the mind, it will tend to work top down at first. As the map gains complexity, new ideas have to be placed on the map where they associate. This part of the process is more creative and right brained, but is constrained by the Basic Ordering Ideas.
Affinity diagrams are a very bottom up right brained process. It starts will a collection of ideas. The goal is not to break an idea apart, or add new ideas, but to find patterns in the ideas available. More analytical thought processes might find affinities based on common nouns in the ideas, but a more creative thought process will find affinities that are not so obvious. Many times the affinities are somewhat goal directed. For example, if you are making affinity diagrams from interview notes on a work process, the affinities should be related to work process. The end goal is creative discovery.
Both mind maps and affinity diagrams can be linearized when done by creating prose or by storytelling. Mind maps work well for deductive and analytical thinking and affinity diagrams work well inductive and synthetic thinking. This is a somewhat stereotypical view. In reality, the mind is not always stuck in one of these modes and there is a blurring effect.
One can also work from linear notes. A mind map can be created by outlining prose. An affinity diagram can be created by segregating sentences and finding themes.
What this means to me is that linear notes, prose, and story telling are good vehicles for communication and capture. Mind maps and affinity diagrams are good tools for processing and creating. Trying to create from linear notes usually means sucking it into a head, working with it there, then spitting it back out into notes. The whole purpose of the tools is to work it as an artifact rather than all in your head. This allows one to solve more complex problems with more than one person.
Story tellers, mind mappers, and researchers each prefer their respective tools. I wonder though how much we constrain ourselves. Tools have built in biases. They are like the electricians tool belt. When you need to strip a wire, pull out the wire strippers. When you need to attach a wire to a plug, bend the wire with pliers, then fasten it with a screw driver. Each problem has its own tool. On the other hand, the tool belt as an whole allows for creative combinations of order of application and combination.
Does the mind really work this way? Does the mind move from tool to tool to solve a problem? Is not the mind an inherently parallel system? Is it not capable of analysis and synthesis at the same time? Yet once we interact with artifacts, the process is sequentialized. All communication and group creation is constrained by the dimensionality of our interfaces and mediums.
I think it is important to recognize that visual processing is highly parallel, compared to listening to someone speak. Even though we are limited to serial interfaces for speaking, writing, and drawing, once a visual artifact is created, the artifact speaks back to a parallel interface. This is what makes models so effective.
To get the most out of visual artifacts requires a dynamic process of creation, listening, and interpersonal interaction. It is the using of all our sensory dimensions, our minds, and our social nature. By extension it is probably best to use multiple models as well, quite possibly at the same time.