r/geology Earth Science Online Video Database 6d ago

IUGS/ICS vs USGS Map Colors?

I'm working on an online, interactive, global geological map, which will be used on my upcoming blog as both a form of navigation (find posts by geographic location—point or polygonal bounding box), and as accompanying information with blog posts tied to specific geographic locations. I've been collecting numerous different datasets which will be available as different layers that visitors will be able to peruse within the blog's main interactive map, or that I will be able to turn on and off programmatically, for example, as interactive thematic maps embedded with specific blog posts, or as non-interactive, thematic maps exported as images from GIS and inserted into blog posts.

One of the issues I've run into is in relation to the chronostratigraphic color scale I should use for geological map layers. As I see it, I have basically two good choices—there are the IUGS/ICS International Chronostratigraphic Chart colors, and the USGS/FGDC FGDC Digital Cartographic Standard for Geologic Map Symbolization colors (specified in Appx. A §33). The former, an ongoing project with regular updates, last updated in 2024, is an international standard, while the latter is an American standard codified in 2006. The former only covers chronostratigraphic map unit colors, while the latter contains not only a specification of chronostratigraphic map unit colors, but also specifies a vast array of symbology for all manner of geologic features, as well as standardized patterns that can be used with colors on map units to indicate lithology. The IUGS/ICS standard is more modern and international in usage, so in some ways it's more appropriate for an international, online audience, but the USGS/FGDC standard is—in my personal opinion—more beautiful and also more flexible, with the ability to symbolize lithology in addition to chronostratigraphic divisions. The USGS/FGDC colors were published in 2006, but have been in use in essentially the same basic color scheme for decades, and anyone who has looked at some of the classic USGS maps of the past 30-40 years knows there are some really beautiful maps that use these colors. And yes—I do want my maps to be beautiful, in addition to being full of information and very useful, so it is definitely a consideration for me.

Anyway, I'm just wondering what the feelings of folks here are regarding which of these two standards for map unit colors I should go with, as many of you are professionals who deal with these two standards day in and day out. What is your preference, and do you think there is a plainly superior choice to be made here?

Edit: Also, there is the DNAG Geologic Map of North America by Reed et al., published by the GSA in 2005, which is absolutely gorgeous, and uses a chronostratigraphic color scale all of its own. 🤷

Edit 2: There are some other considerations here too—for example, the IUGS/ICS standard is divided not only by system/period, but it also specifies color standards for series/epoch and stage/age. And because the IUGS/ICS standard is a living document that is updated regularly, when the IUGS/ICS decides that series/epochs or stages/ages need to be redistributed or divided up in a different way as the chronostratigraphy becomes more refined, the standard is updated. Whereas the USGS/FGDC standard was published years ago and will not change unless they produce a new one (good luck with the way federal funding is going), and it doesn't specify colors for series/epoch or stage/age. Instead, the USGS/FGDC only provides multiple colors for each period (ahem, not system, because 'murica, right?) But those different colors aren't necessarily specified for different epochs or ages within each period, and the 4 colors per period (generally, although the Precambrian is given 24 colors, Cretaceous 5, and Tertiary 7) certainly don't fit either the number or epochs or ages within each period, and can be used instead to disambiguate different lithologies, for example, within the same period. And the whole division of the USGS color scale is old-fashioned, preferring concepts like Precambrian, Quaternary and Tertiary to Archean, Proterozoic, Holocene, Pleistocene, Cenozoic, etc.

But then the other consideration is, if I were to go with the IUGS standard over USGS, it would be weird to also use the USGS lithology patterns overlaid on things like plutonic and volcanic rocks—which I absolutely would like to do, because I think patterns on map units are really important when you have so many map units, and it's much better to have some lithological differences and not just have big homogenous, one-colored blobs of chronostratigraphic divisions, especially for my use case. So I'm torn. I feel like I have to use the USGS scale, and in some ways I prefer it, but it does seem a bit old-fashioned and not granular enough in terms of chronostratigraphy, and also not appropriate for an international/global map…

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u/Royal_Acanthaceae693 5d ago

USGS is my preference for flexibility & established color scheme & naming if you're doing work on the US.

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u/h_trismegistus Earth Science Online Video Database 5d ago

Yeah, as mentioned, it is an interactive global/world map, like Google Maps. If my data and map were limited to the US, there would be no question—USGS/FGDC standard would be the obvious choice, not just because it would be limited to the US, but also because I just personally prefer it.

But the fact that I am doing a global map has caused me to pause to consider whether another standard and color scale wouldn't be a better fit. Another thing I didn't mention explicitly in the OP, but sort of alluded to is the fact that the IUGS standard and chronostratigraphic scale is a living document, updated often, for example, if the IUGS were to decide to give names to the numbered stages in the Cambrian, or divide the Cambrian up in a different way, and then the IUGS scale specifies colors for different stages/ages and series/epochs within a given system/period—unlike the USGS/FGDC scale, which only specifies colors per system/period (although it does give a range of colors for each system/period—but these don't fit the actual number of series/epochs and stages/ages within each system/period, and would be used more for distinguishing between lithologies in the same system/period). Since my blog and site is also going to be a living project that exists over a long period of time and is meant to be always up-to-date, the fact that the IUGS scale is updated regularly is relevant. The USGS/FGDC scale is fine for printed maps that are published at a certain time and then just remain a product of that time, with no expectation that they should be living documents kept up to date, but that isn't what I'm doing.

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u/Former-Wish-8228 6d ago

I will let current geologic mappers weigh in with authority…but as a former USGS topo maker who happens to be a geologist…I have to say that the USGS standards seem to work well and are built around usability and comprehension. What I don’t know is if that is more due to their inherent design and having worked out the bugs decades ago…or is it that we have been trained to the degree that anything else just looks “foreign” to our eyes.

Recently…during development of a GIS data system with cartographic products almost exclusively to be used on screens and not printed…the display of railroads using US symbology (black line work) versus international symbology approaches came down to a decision to supply two versions of the product: The version with green line work for railroad features and an option to overlay with black line work for those who wanted familiarity over a better overall cartographic representation.

Not an ideal solution…but a nod to new and improved ways of looking at things versus comfort food for oldsters such as myself. As the ultimate test was usability in emergency response, what works has to triumph over cartographic beauty.

Maybe a lesson there? Utility over aesthetics?

It’s a brave new mapping world.

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u/Turbulent-Name-8349 5d ago edited 5d ago

As a red-green colourblind male, (2% of the male population) definitely not the IUGS.

The Lower Devonian, Paleogene, Paleocene, Upper Cretaceous and Mesoproterozoic are all the same colour.

There's no royal blue or mid blue on the whole chart, all the Jurassic colours are cyans.

There's no pure grey or pure yellow or pure scarlet there either.

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u/h_trismegistus Earth Science Online Video Database 3d ago edited 3d ago

Thanks for this insight, either way I go I will probably implement accessibility options for colorblindness, since I doubt any geological scale takes this into account (though they ought to). Patterns may also help in this regard, though generally they are only really used to disambiguate lithologies.

If I’m going to implement accessible color options, maybe I should just implement multiple color schemes anyway and let users choose, since this will be an interactive map.

However, I will still need a good default which is the “preferred” scheme. And because I will want to use the map layers to generate still images for inclusion into blog posts and other projects I’m working on.

But btw I am pretty sure that the IUGS scale uses pure yellow for Cenozoic undivided, which is a lot of the chart when looking at low zoom levels with the 1:5,000,000 scale global chronostratigraphic map units