How do you classify type A vs. typeB vs. typeC neighborhoods

[Asim G.]

Hi,

I have been bouncing around on BP for a few months and have learned a tremendous amount about RE investing. However, I still get a little confused when people refer to A/B/C/D neighborhoods. I guess like all terminology, some of it is random and depends on the whims of the user. 

At the same time RE investors use it to communicate area types with each other frequently so there must be some system to it.

Can the experts here share with me their mental process of classifying properties. I think I understand what Type A and D are. My biggest confusion is separating the B's from the C's

Thanks