@Mark Manig In the top right of the page there is a search bar and if you search for the topic of neighborhood classes you can find a ton of information posted on the topic over the years on the forums, blogs, articles on the topic, etc...
There is no accepted classification that I know of, as to tenants, I can see basic loan assumptions being made, unqualified, marginal, qualified, well qualified and strongly or extremely qualified.
Just posted in a thread 45K in a C or 55K in an A something like that around post 65.
I can think of 10 clearly defined classifications of neighborhoods, from million dollar golf course types down to 20K depressed areas. Can't describe them to convey any real meaning defined in 4 classifications. To many variables would be left out with 4 classifications.
Cost alone is not a determining factor, neither is size or if yards are mowed every 5 days. :)