Is there a categorical scale used to interpret values from the Terrain Ruggedness Index as calculated by Wilson et al. (2007), which is used in the raster library in R?

  • It helps if you can link to cited research, saves us tracking down the articles!
    – Spacedman
    Sep 12, 2021 at 15:14

1 Answer 1


The paper by Riley et al (1999) cited by the Wilson et al paper has a map with seven categories of ruggedness (and an odd colour scheme but whatever)...

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They use an "equal area" basis for the breakpoints, which I guess means they were chose so that each category is the same area on the map, which seems a bit arbitrary but unless you have some idea of what "rugged" means then I guess its as good as any other...

  • I'm looking at these values for southern Arizona. So if I divide the range of values in my map into 10 categories, then that would give me a relative categorical scale I could use to assign to values I sample from points in the area? Sep 12, 2021 at 17:15
  • That's what they do in the paper, but with 7 categories, with the breaks in the categories set so that exactly 1/7 of the area is in the "Level" category, 1/7 in "Nearly Level" and so on. For any vector of values z you can get the breakpoints for 7 categories with quantile(z,seq(0,1,len=8)) - but the category definitions will be different for Arizona if you work them out for Nebraska.
    – Spacedman
    Sep 12, 2021 at 19:51

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