Colors on the Geologic Map

I noticed on my Stats page that some folks found my post about displaying the Geologic Atlas of Texas information in Arcmap. So I felt compelled to search for a solution to my problem. Whether you are a geologist or not, you may know that on geologic maps rocks of certain ages are by convention displayed in certain colors, i.e. Permian rock is usually blue and Creteceous rocks are green. North Central Texas, entirely of Cretaceous rock, is therefore green on the map, except for streams and rivers whose flood plains are displayed in yellow because they’re filled with Quaternary fluviatile and alluvial deposits. (I’m bound to say something wrong any moment now. So if any smarter geologists are reading this right now, please forgive me, I’ve been out of school for 10 years, and I work with engineers.)

The coloring conventions are old, and although I got my degree in Europe, I couldn’t tell you right now how international they are. My problem with the colors on the map was that ArcMap is great at giving you a cornucopia of possible colors and patterns to display your geologic information. But that’s precisely not what you need because by convention certain rocks should be in certain color. Digging a little deeper, I found this page at the Federal Geographic Data Commitee (FGDC) for a Digital Cartographic Standard for Geologic Map Symbolization. There’s a starting point !

This standard goes through every kind of geologic map element and proposes how it should be displayed on a standard map. Section 33  provides examples of how rocks of certain age should be colored. Another related document from the United States Geological Survey has a nice chart with colors for the geologic time scale. I guess I need to create my own color scheme for North Texas using the proposed standards and conventions now. Unless I still get lucky and find that someone’s done so and posted it online. The FDCG website mentions an ESRI version of this standard that’s in the works.

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