As a follow on from here: http://stats.stackexchange.com/questions/69810/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.