Research in spatial cognition offers a wide spectrum of possibilities to combine psychological and computational approaches. Sometimes, the design of computational systems may merely be based on what researchers believe happen in their minds when solving spatial reasoning problems. In other cases, an already existing computational approach is enabled post hoc as cognitively adequate, or psychologically valid. In the contribution, it will be argued that carefully conducted experiments with human participants are needed to understand spatial cognition. Based on such experiments, the contribution will then clarify the role of visual images and spatial representations in human reasoning and problem-solving. What is represented in such representations? Visual features such as color, shape, texture, etc? Spatial information such as topological, metrical, or ordinal relations? Then the contribution will provide experimental evidence on which kind of information should be presented in diagrams so that they efficiently support reasoning processes in humans and technical systems, as well as in human-machine interaction. Finally, it will provide some thought on why reasoning could be so inextricably connected to the cognitive representation and processing of space.