There are many different ways of thinking about gaps in knowledge. Engraved on the copper face of the Lenox Globe c.1500, one of the oldest known terrestrial globes, are the evocative words: ‘‘here be dragons’’ . This was used by cartographers to signify dangerous or unexplored territories and drew on a long history from classical times when lack of knowledge equated to danger. This danger was illustrated visually by filling blank areas of maps with fierce looking sea serpents, dragons or mythological creatures to warn travellers of the risks they might face. For any user of the map, understanding where the boundaries of knowledge lay was almost as important as knowledge itself. Illusion of knowledge was the greatest danger of all.