[nonameiguess]

It's oversimplified for any region whatsoever. You're citing right here what people speak like in big west coast cities but I grew up in California and would have been able to tell apart people who grew up in Anaheim versus San Gabriel Valley versus San Fernando Valley versus West LA, let alone LA versus San Francisco. I couldn't have explained what the difference is but I could have heard it. Everybody will be more attuned to the tiny regional differences of the place they actually come from, but a map like this would be impossible to make if you tried to draw out the boundaries and explanations for 400 million separate regional dialects.