How you categories an area class as A/B/C/D? Is it depended on the area?

[Justin Brin]

How you categories an area class as A/B/C/D? Is it depended on the area?

Can you tell an area class just by viewing it from street view?

I'm guessing in some cities an area can be dirty with homeless but with high prices and high rents (Like in some areas in Los Angeles). While some areas can be class C with lower cost and lower rents but clean and no homeless.

Some areas can have not such good schools but prices are high and rents are high while other areas can have good schools and prices and rent are not that high.

How will you best define an area as class A-D?