Plotting lineament strikes/trends on a Rose diagram

Hi everyone! Our last post was about calculating lineament strikes using GIS. Check out that post here: https://adgeos.blogspot.com/2020/03/Calculating-fault-strike-using-GIS.html

Note: When dealing with digital structural data, azimuthal bearing is the convention of choice. If you are used to quadrantal bearing, slowly re-familiarize yourself with the azimuth concept, as it is much simpler to encode.

This time, I'll be showing you how to plot the strikes you calculated in informative Rose diagrams. If you don't know what a Rose diagram is, it's a way to represent directional data by emphasizing which directions are most common in a dataset. The most frequent directions are represented by long bars emanating from the center of a circle, while less frequent directions are represented by shorter bars. You can think of it as a circular histogram.



Here's an example from the simple Rose diagram plotting software GeoRose:

Within a quadrant, there are 6 bars. A quadrant is equal to 90°, so each bar should be 15° wide. You can see the longest bar is generally along the direction of 045°/225°. This is because many of the data points (shown in the table on the left) are within +-7.5° of this direction.

If you only have a few datapoints, say 20, I suggest you use GeoRose because of its simplicity. There are many options to change the design, i.e. the bar color, labels, size, bar width, background color etc.

However, if you have a large dataset, I suggest you export the attribute table from your GIS software. Reformat it so that it only contains the data you need (strikeCor, if you base it on the previous post) and copy-paste it on a .txt file with the first line being the header "TP". Unfortunately, GeoRose does not import text files, so you will have to use something else. A good alternative is the free software Stereonet programmed by the great Richard Allmendinger (just search for his website and programs on Google). 

"TP" is just a code created by Allmendinger to refer to the syntax of the input data: Trend-Plunge, hence TP. But since we're only dealing with strike values (no plunge or dip), we only need to input one value per line in the .txt file. If you want to know more, just click on the Help option when you open the Stereonet program to open the manual, as you can see below.

There's much more you can do with Stereonet, in terms of the types of calculations and analyses you want. One simple example is the black arrow in the figure above. It represents the mean vector, basically the average direction, of the dataset, and can be calculated and displayed by the software with the click of a button. 

But the design options of Stereonet are limited. This is why I stick with GeoRose as much as I can. I only bust out Stereonet when I know I need to conduct a more in-depth analysis of my data.

Alright that's it, let me know in the comments if you have any questions. Good luck fellow AGs!