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.