How do experienced users extract information from a complex visualization? We examine this question by presenting experienced weather forecasters with visualizations that did not show the needed information explicitly and examining their eye movements. We replicated Carpenter & Shah (1998) when the information was explicitly available on the visualization. However, when the information was not explicitly available, we found that forecasters used spatial reasoning in the form of spatial transformations. We also found a strong imagerial component for constructing meteorological information.