Visualizations of 3D spatial structures use various techniques such as user controlled interactions or 2D projection views to convey the structure to users. Researchers have shown that motion cues can help assimilate the structure of 3D spatial data, particularly for discerning occluded parts of the objects. However, motion cues or smooth animations also have costs - they increase the viewing time. What remains unclear is whether any one particular viewing modality allows users to understand and operate on the 3D structure as effectively as a combination of 2D and 3D static views. To assess the effectiveness of understanding 3D structures, we carried out three experiments. In all three experiments we evaluated the effectiveness of perceiving 3D structures with either self controlled interactions, animated transitions, and 2D+3D static views. In the first experiment, subjects were given a task to estimate the relative distances of objects in a 3D scene. In the second experiment, subje...