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The Lagrangian analysis of particulate matter, biota and drifters, which are dispersed by turbulent fluid currents, is a cornerstone of oceanographic studies, covering diverse study objectives. The results of Lagrangian simulations and observations is predominantly visualised by means of easy-access plotting interfaces and simple presentation techniques. We analysed over 50 publications from the years 2010-2020 with respect to their visual design to deduce common visualisation practices in the domain. Individual figures are analysed towards adherence to visualisation best-practices, algebraic visualisation guidelines and the IPCC visual style guide. In this article, we present the resulting best-practices and common pitfalls in the design of Lagrangian ocean visualisations. Based on this visual study, we highlight that raising awareness of established visual guidelines may have a higher impact on improving the visual quality of publications in oceanography than the vigorous development of more general-purpose visualisation tools.

Understanding complex systems (CSs) is an important skill in science education that is characterised by the ability to interrelate multiple scales of information. Visualisations play a significant role in supporting this cognitive skill by externalising these complex interrelationships into a perceptible form. However, the information at each level of a CS, from the agent (micro) to the aggregate (macro), may be best conveyed using different types of representations, making it difficult for individuals to visually and conceptually link the multiple levels of the system. The aim of this thesis is to investigate how to optimally design visualisations to improve student understanding of CSs. In particular, for CSs in which the physical structure directly influences its behaviour and function, and where changes enacted at a level higher than the agent have implications for all levels of the system. Following a visualisation design system approach, the investigation was divided into two phases. Phase I involved two user studies that examined student-generated external representations (ERs) of a CS to assess their understanding and type of representations they associated with the system. The findings from Phase I were used to formulate a set of preliminary design principles that were applied in Phase II, the instantiation and evaluation of the design principles in functional prototype visualisations. The design principles, and corresponding prototype visualisations, underwent two iterative cycles. Students struggled with the first version of the prototype that integrated the student-generated ERs from Phase I, demonstrating a conceptual disconnect between structural, behavioural, and functional elements within and between the agent and aggregate levels of the system. These student difficulties necessitated a revision of the preliminary design principles, informing changes in the type of ERs and visualisation transition techniques to be used in the second prototype. Studen