Maps are visual design representations used by engineers to model the information behind a design. This paper evaluates the application of mapping methods supported by the Decision Rationale editor (DRed) in aerospace engineering industry. Specifically, the research investigates what DRed mapping methods are used, where engineers find them useful and why. DRed was selected because it has been formally embedded in the design processes of the partner company and all engineering staff have access to it. The tool was investigated using semistructured interviews with 14 engineers, each already trained with DRed through their work and representing diverse departments and experience levels. Nineteen use cases were collected, ranging from high-profile, multistakeholder projects to everyday individual work. Collected cases were analyzed for the methods applied, common contexts of use, and reasons for use. The results validate baseline DRed mapping methods to capture design rationale and analyze the root causes of engineering problems. Further, it provides empirical evidence for new DRed mapping methods to manage requirements, analyze functional interactions in complex systems and manage personal information. The contexts where mapping methods are most used involve: system-level information that cuts across subsystem boundaries; irregular intervals between map applications; dealing with loosely structured information; individual use or small team collaborations; and addressing on-going problems. The reasons stated by engineers for using maps focus on engineering design thinking, communication, and planning support. Using empirical evidence of its recurrent use, this research establishes that DRed is a powerful and versatile tool for engineers in industry and its mapping methods aid important and otherwise unsupported work. The range and impact of the use cases found in practice suggest that engineers need better support for work with loosely structured information. Organizations involved in the design of complex systems should make greater use of semiformal, graph-based visual tools like DRed. The understanding of mapping software gained through this research demonstrates a shift in emphasis from the enrichment of the engineering record to the provision of immediate cognitive benefits for engineers. The results also support an incremental, adaptive approach for deploying this emerging class of tools in other organizations.