A while ago, I randomly bought a used copy of “Le Macroscope” by Joel deRosnay (1975), a book about systemic analysis and the study of complex systems. Right from the start, the theories striked me as powerful game design tools.
A complex system is a group of “entities” bounded by a network of interactions, trying to keep the system in balance. Examples of complex systems: the ecosystem, the economy, a city, a corporation, a beehive, etc.. The interactions in a complex systems follow one or many sets of rules and have one or many “centers of decision”.
Look at these illustrations (01, 02) from “Le Macroscope” representing different sets of rules found in nature. The ressources, processes and movements within the models are all identified visually. The systems, stripped down to their essentials, are easy to visualize and understand.
Note: I encourage you to at least read the first chapter of this excellent book. It is the most practical part of the book and gets you started quickly.
With the help of this kind of schemas, I worked on and idea about interplanetary politics and trades (at first I intended to create a simple background mechanic for a Flash game but it evolved into a board game). I quickly pinned down the most important aspects of the game, named them and depicted possible interactions. After a few sketches, I came up with something coherent with all the details I wanted. Here is the resulting model (my model is more akin to deRosnay's model about simple economies).
With a clear and understandable model, I went on to create the pieces of my board game and wrote the rules. At this point, all the important mechanics and most of the gameplay details were in place. Illustrating the desired system helped me visualize it and gave me a better understanding of the decisions the players will have to take. After all, this is what games are: complex systems.