This chapter draws attention to case studies of scientific discovery as an important source of information about visualisation as a real-time cognitive process. These show that visual modes of representation are essential to the generation, communication and dissemination of new knowledge. I survey a number of strategies of visualisation and develop a process model based on the ways that scientists in a wide range of fields manipulate the dimensionality of images in order to move between representations that are local, situated and often personal and images that are widely understood and have an objective status as depictions of facts or laws. This shows that the cognitive status of visual images changes as scientists integrate novel representations into their arguments.