Was browsing an old Teaching History and saw an article by Steve Garnett which have immediately stolen! It’s really simple and really effective. Basically, a large circle in the centre of a page represents a concept, e.g Bismarck’s foreign policy (Steve’s example) or the Break with Rome (my example attached). Other circles placed strategically, in terms of size and location, represent key influences on that issue. Could also be used for effective essay planning.