Rainbow colour maps are known to be problematic yet remain widely used in scientific communication. This study extends work by Stoelzle and Stein (2021) to investigate the extent of their use in geoscience publications. It is found that over half (55 %) of all papers surveyed from six geoscience journals from the years 2005, 2010, 2015 and 2020 (n=2638) contained at least one visualisation that uses rainbow or red–green colour schemes and are therefore potentially misleading and colour-inaccessible. Recent changes to the submission guidelines for all European Geosciences Union (EGU) journals would seem to place greater responsibility in the future with editors and reviewers to identify and correct colour issues as part of the review process

Westaway, Richard M.

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Westaway, Richard M

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GC Insights: Rainbow colour maps remain widely used in the geosciences

Rainbow colour maps are known to be problematic yet remain widely used in scientific communication. This study extends work by Stoelzle and Stein (2021) to investigate the extent of their use in geoscience publications. It is found that over half (55 %) of all papers surveyed from six geoscience journals from the years 2005, 2010, 2015 and 2020 (n = 2,638) contained at least one visualisation that uses rainbow or red-green colour schemes and are therefore potentially misleading and colour inaccessible. Recent changes to the submission guidelines for all EGU journals would seem to place greater responsibility in the future with editors and reviewers to identify and correct colour issues as part of the review process

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                          Westaway, R. M. (2022). GC Insights: Rainbow colour maps remainwidely used in the geosciences. Geoscience Communication, 5(1),83–86. https://doi.org/10.5194/gc-5-83-2022Publisher's PDF, also known as Version of recordLicense (if available):CC BYLink to published version (if available):10.5194/gc-5-83-2022Link to publication record in Explore Bristol ResearchPDF-documentThis is the final published version of the article (version of record). It first appeared online via CopernicusPublications at https://doi.org/10.5194/gc-5-83-2022.Please refer to any applicable terms of use of the publisher.University of Bristol - Explore Bristol ResearchGeneral rightsThis document is made available in accordance with publisher policies. Please cite only thepublished version using the reference above. Full terms of use are available:http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/Geosci. Commun., 5, 83–86, 2022https://doi.org/10.5194/gc-5-83-2022© Author(s) 2022. This work is distributed underthe Creative Commons Attribution 4.0 License.GCInsightsGC Insights: Rainbow colour maps remain widely usedin the geosciencesRichard M. WestawayBristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UKCorrespondence: Richard M. Westaway (r.westaway@bristol.ac.uk)Received: 15 October 2021 – Discussion started: 26 October 2021Revised: 4 February 2022 – Accepted: 8 February 2022 – Published: 11 March 2022Abstract. Rainbow colour maps are known to be problem-atic yet remain widely used in scientific communication. Thisstudy extends work by Stoelzle and Stein (2021) to inves-tigate the extent of their use in geoscience publications. Itis found that over half (55 %) of all papers surveyed fromsix geoscience journals from the years 2005, 2010, 2015 and2020 (n = 2638) contained at least one visualisation that usesrainbow or red–green colour schemes and are therefore po-tentially misleading and colour-inaccessible. Recent changesto the submission guidelines for all European GeosciencesUnion (EGU) journals would seem to place greater responsi-bility in the future with editors and reviewers to identify andcorrect colour issues as part of the review process.1 IntroductionData visualisation is a crucial aspect of geoscience commu-nication, and decisions about how colour is used to visualisedata are influential in defining which messages are communi-cated to the reader (Zeller and Rogers, 2020). The availabil-ity of low-cost or free programming and visualisation tools,combined with the rise of online delivery, has created muchgreater freedom in the use of colour to encode maps andgraphs in scientific journals. However, the encoding accuracyof colour has been criticised, particularly with respect to therainbow (or jet) colour map (Rogowitz and Treinish, 1998;Borland and Taylor, 2007; Liu and Heer, 2018; Crameri etal., 2020). In general, these criticisms relate to (i) the concur-rent use of red and green, which are hard to distinguish forup to 4 % of the global population with colour vision defi-ciency (CVD) (Light and Bartlein, 2004; Nuñez et al., 2018),and (ii) its tendency to exhibit non-uniform luminance acrossits length, which disproportionately, and in some cases mis-leadingly, draws attention to the yellow and cyan elements(e.g. Rogowitz and Treinish, 1998; Borland and Taylor, 2007;Hawkins, 2018).While it is now considered best practice to avoid rain-bow or quasi-rainbow colour maps (Crameri et al., 2020),they remain widely used in geoscience communication (e.g.McNeall, 2018; Zeller and Rogers, 2020), perhaps in largepart due to the “inertia” of scientific communication, wherewidespread use of rainbow colour maps is a reason why sci-entists propagate it further (Moreland, 2016). A recent sys-tematic review of around 1000 scientific publications fromthree different journals by Stoelzle and Stein (2021) con-cluded that 16 %–24 % of the publications used a rainbowcolour map, with a similar proportion (18 %–29 %) usingred–green elements without an alternative way of distin-guishing them, meaning that approximately one in every twopapers has colour issues.In this study, I adopt a similar approach to Stoelzle andStein (2021), extending their analysis to other geosciencejournals, to investigate the use of rainbow and red–greencolour schemes across different geoscience disciplines.2 MethodsI undertook a manual survey of papers published in fourEuropean Geosciences Union (EGU) journals – Earth Sys-tem Dynamics (ESD), Ocean Science (OS), Solid Earth (SE)and The Cryosphere (TC) – and one American Geophysi-cal Union (AGU) journal – Geophysical Research Letters(GRL). For the four EGU journals, all papers published in2005, 2010, 2015 and 2020 were considered. For GRL, arandom sample of 200 papers was selected for each of thesePublished by Copernicus Publications on behalf of the European Geosciences Union.84 R. M. Westaway: GC Insights: Rainbow colour maps remain widely used in the geosciencesyears. In total, 1841 papers were surveyed from these fivejournals. An exact breakdown of how many papers were sur-veyed from each journal for each year is given in Fig. 1.Following the approach of Stoelzle and Stein (2021), pa-pers were classified using a four-way classification.i. Black and white paper with no colour visualisationsii. No rainbow colour or red–green visualisations or, ifused, unambiguous interpretation possible with ele-ments or labellingiii. At least one visualisation with rainbow-related colour-ing or red and green elements without an alternative (i.e.non-colour-based) way of distinguishing themiv. At least one visualisation that uses a rainbow colourmapSubsequently, classes (iii) and (iv) are collectively re-ferred to as papers with colour issues, i.e. those containingambiguous or non-CVD-friendly visualisations. When com-bined with the 797 papers surveyed by Stoelzle and Stein(2021) from the EGU journal Hydrology and Earth SystemSciences (HESS), this produced an overall data set of 2638papers spanning a range of geoscience disciplines.3 ResultsOverall, 34 % of the papers surveyed were found to haveat least one visualisation with a rainbow colour map, witha further 21 % containing a figure that used red–green el-ements. This means that over half (55 %) of all the paperssurveyed contained at least one visualisation with colour is-sues (Fig. 1). Compared to 2005, the number of papers usingrainbow colour schemes in 2020 was found to be relativelyconsistent (31 % in 2020 compared to 29 % in 2005), thoughthe proportion was greater in the intervening years (reachinga maximum of 38 % in 2010). There is a similar pattern whenpapers containing red–green elements are included, with thetotal proportion of papers with colour issues increasing from37 % in 2005 to a peak of 61 % in 2015 before falling slightlyto 55 % in 2020.Comparing across the different journals, OS was found tocontain the most papers that used rainbow colour maps, with59 % containing at least one rainbow colour image and 75 %containing visualisations with colour issues. It was found thatin every journal considered, except for HESS (44 %), overhalf of all the papers surveyed contained at least one visu-alisation with colour issues and, even as recently as 2020,more than half of the papers published in GRL (59 %), OS(76 %) and SE (76 %) used rainbow or red–green visualisa-tions. The largest reduction in the use of rainbow colour mapswas found to be in ESD, in which the proportion of paperscontaining at least one such visualisation reduced from 33 %in 2015 to 10 % in 2020, albeit based on a smaller samplesize than for the other journals (n = 46 in 2015; n = 69 in2020).4 DiscussionDespite widespread recognition of the weaknesses of rain-bow colour maps and of the wider issues associated with theuse of red–green colour schemes, the results of this studysuggest that both continue to be widely used in geosciencepublications. The results presented here, in line with Stoel-zle and Stein (2021), suggest there was a slight reductionin the use of data visualisations with colour issues in 2020.There are perhaps three main reasons for this. First, aware-ness of the issues associated with rainbow colour maps hasgrown. For example, the Crameri et al. (2020) paper “Themisuse of colour in science communication” was the second-most downloaded Life and Biological Science article pub-lished in 2020 from Nature Communications (Nature Com-munications Collection, 2021). Second, more tools and re-sources have become available to support better decision-making with respect to colour schemes. For example, Stoel-zle and Stein (2021) propose four actionable techniques toimprove the use of colour in scientific communication, whilethe Scientific colour maps package (Crameri, 2021) has beendownloaded more than 4700 times since 2018, with the lat-est version (7.0, released in February 2021) accounting formore than half of this total. Third, more journal publishers,editors and reviewers are now identifying colour issues atmanuscript submission stage and requesting changes to pa-pers that contain them (see further discussion below). De-spite this, over half of the geoscience papers surveyed from2020 still contain at least one visualisation that was ambigu-ous or non-CVD-friendly, and any improvement from previ-ous years appears to be uneven across different geosciencejournals and so, by implication, across different geosciencedisciplines.The continued proliferation of papers with problematiccolour schemes can perhaps be explained, at least in part, bythe relative lack of guidance provided by many journals toauthors about the use of colour in visualisations. For exam-ple, no guidance on the use of colour schemes was found inthe “Resources for authors” provided by the AGU for sub-mission to GRL, including in its “Graphics requirements”(AGU, 2021), nor in the standard EGU “Manuscript prepara-tion” guidelines used up until 2015 (e.g. Ocean Science viathe Wayback Machine Web Archive, 2015). In such cases,there is a clear opportunity (and perhaps even obligation) forjournal editorial boards and publishers to make authors moreaware of colour issues or to go further by specifically advis-ing against the use of rainbow and red–green colour scales intheir publications (Stoelzle and Stein, 2021).From 2015 until 2021, the EGU standard submissionguidelines were amended to include advice against parallelusage of red and green in maps and charts (e.g. Ocean Sci-Geosci. Commun., 5, 83–86, 2022 https://doi.org/10.5194/gc-5-83-2022R. M. Westaway: GC Insights: Rainbow colour maps remain widely used in the geosciences 85Figure 1. Proportion of papers surveyed with and without colour issues. Journals considered were Earth System Dynamics (ESD), Geo-physical Research Letters (GRL), Ocean Science (OS), Solid Earth (SE) and The Cryosphere (TC) for the years 2005, 2010, 2015 and 2020.Results obtained by Stoelzle and Stein (2021) for Hydrology and Earth System Sciences (HESS) are also included.ence via the Wayback Machine Web Archive, 2021), thoughthis single mention in otherwise lengthy guidance text couldhave been potentially easily overlooked. The EGU submis-sion guidance was further updated in 2021, with more infor-mation and resources presented prominently at the start of the“Figures & tables” section and with consideration of colourschemes included in the “Get ready” submission checklist(e.g. Ocean Science, 2021). In addition, authors are asked toconfirm during the manuscript submission process that thecolour schemes used are accessible to people with CVD. Itremains to be seen whether these changes will, in future, re-sult in a reduction in the number of papers in EGU journalscontaining visualisations with colour issues, but at the veryleast it would appear to place increased responsibility witheditors and reviewers to identify and correct colour issues aspart of the review process.Data availability. The survey data set compiled here is avail-able online at https://doi.org/10.5281/zenodo.5566884 (West-away, 2021). This data set includes the existing Stoelzleand Stein (2021; https://doi.org/10.5194/hess-25-4549-2021) sur-vey data for HESS, which is independently available athttps://doi.org/10.5281/zenodo.5145746 (Stoelzle, 2021).Competing interests. The contact author has declared that thereare no competing interests.Disclaimer. Publisher’s note: Copernicus Publications remainsneutral with regard to jurisdictional claims in published maps andinstitutional affiliations.Acknowledgements. I thank Michael Stölzle for his helpfulcomments on an early draft of this paper and Fabio Crameri andan anonymous reviewer for their subsequent comments on the sub-mitted manuscript.Financial support. The work was supported by the European Re-search Council (ERC) under the European Union’s Horizon 2020research and innovation programme under grant agreement no.694188 (GlobalMass).https://doi.org/10.5194/gc-5-83-2022 Geosci. Commun., 5, 83–86, 202286 R. M. Westaway: GC Insights: Rainbow colour maps remain widely used in the geosciencesReview statement. This paper was edited by Leslie Almberg andreviewed by Fabio Crameri and one anonymous referee.ReferencesAGU: Graphic Requirements, https://www.agu.org/Publish-with-AGU/Publish/Author-Resources/Graphic-Requirements, last ac-cess: 13 October 2021.Borland, D. and Taylor, R.: Rainbow Color Map (Still)Considered Harmful, IEEE Comput. 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S.: Optimizingcolormaps with consideration for color vision deficiency to en-able accurate interpretation of scientific data, PLoS ONE, 13,e0199239, https://doi.org/10.1371/journal.pone.0199239, 2018.Ocean Science: Submission guidelines, https://www.ocean-science.net/submission.html, last access: 13 October 2021.Ocean Science via Wayback Machine Web Archive: Manuscriptpreparation guidelines for authors [as they appeared on 29 March2015], http://web.archive.org/web/20150329164339/http://www.ocean-science.net:80/for_authors/manuscript_preparation.html(last access: 13 October 2021), 2015.Ocean Science via Wayback Machine Web Archive: Manuscriptpreparation guidelines for authors [as they appeared on 18September 2021], http://web.archive.org/web/20210918053545/https://www.ocean-science.net/submission.html#figurestables,13 October 2021.Rogowitz, B. E. and Treinish, L. A.: Data visualization:the end of the rainbow, IEEE Spectrum, 35, 52–59,https://doi.org/10.1109/6.736450, 1998.Stoelzle, M.: Rainbow color map distorts and misleads re-search in hydrology – guidance for better visualizationsand science communication (v1.0), Zenodo [data set],https://doi.org/10.5281/zenodo.5145746, 2021.Stoelzle, M. and Stein, L.: Rainbow color map distorts and misleadsresearch in hydrology – guidance for better visualizations andscience communication, Hydrol. Earth Syst. Sci., 25, 4549–4565,https://doi.org/10.5194/hess-25-4549-2021, 2021.Westaway, R. M.: Rainbow colour maps remain widelyused in the geosciences (v1), Zenodo [data set],https://doi.org/10.5281/zenodo.5566884, 2021.Zeller, S. and Rogers, D.: Visualizing science: Howcolor determines what we see, Eos, 101, 28–35,https://doi.org/10.1029/2020EO144330, 2020.Geosci. Commun., 5, 83–86, 2022 https://doi.org/10.5194/gc-5-83-2022

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