As a follow on from here: Correlation between vegetation and erosion, I am having some trouble with the type of data that I have. I am confused as to whether my four categories are ordered. Specifically, my four groups within my categorical variable are: vegetation loss, no change non vegetated areas, no change in vegetated areas and vegetation gain. While they are in order of an increasing amount of vegetation, I'm not sure if they would be considered nominal or ordinal. Any advice appreciated.