I believe the classes are based on how 'ideal' the location is. I do not think it is at all related to something being 'plot one'. Plot numbers are just where the plots are located. I'm not sure exactly WHICH plots are class one, class two, etc. You'll be able to tell when the servers go up. Just go look at the plots. Hurry, though, because FCs may be looking out to snag them ASAP. Happy hunting!