We expected planners working on the planning problems at a particular department for many years to have similar ideas about their work domain. However, we found the opposite when we analyzed the results of an extensive knowledge elicitation study we performed on 25 planners working in the rolling stock and rolling staff planning department of the Netherlands Railways (in Dutch: NS). The planners were asked to model their domain by means of card sorting and graph-positioning methods using domain-related objects and relations. When we applied multi dimensional scaling to the outcome of this study, we found large differences in the individual cognitive maps thus created. In this article, we describe the analyses and discuss our findings about planners' cognitive maps. These maps may have implications for the organization of planning in general, for training of planners, and for software design. (c) 2005 Elsevier Ltd. All rights reserved.