Objective versus subjective measures of metro map usability: Investigating the benefits of breaking design rules.

Schematic maps are an important component of assistance for navigating transport networks worldwide. By showing routes as simple straight lines, they reduce the cognitive load of journey planning, and by revealing the underlying structure of networks, they make their key features easier to identify and learn. However, although there are many suggestions for optimizing schematic maps so as to maximize these benefits, to date these have not been directly supported by published usability studies or psychological theory. In this paper, we suggest that there are circumstances in which conventional schematic maps fail to yield benefits, and we compare journey planning using the current official RATP Paris Metro map with an All-Curves design which replaces straight lines and corners with gentle curves. Three separate usability studies with slightly different methodologies showed that the journey planning time for the All-Curves map was better then the RATP version, with effect sizes ranging from 0.48 to 1.12. Subjective usability ratings were derived from questionnaires, and user preferences, but neither were correlated with objective usability measures. We conclude that (1) in terms of designing schematics, there is no evidence to suggest that any rule-set can be claimed to be a gold-standard, and it is important to match the design rules to the properties of the network, (2) in some circumstances, radical departures from traditional ideas can yield usability benefits, and (3) map usability appears to be distinct from map engagement, although the latter is undoubtedly important in encouraging people fully to make use of navigation aides.