Now, some areas of the US have relatively few native speakers of Spanish in them. There are certain areas - and I'm sure some of them would surprise me - where there are concentrations, strong communities of Spanish speakers.
My assumption is that, those communities/concentrations are largely uniform in what kind of Spanish is spoken - that there are more likely to be, for examples groups of Puerto Ricans, in which a Mexican would stand out almost as much as a Spaniard, than there are to be communities which contain many different national variations. In other words, I'm assuming that there are cultural connections grouping people together in those communities, as well as language, and that language 'stands in' for culture in a lot of ways.
If anyone has personal knowledge to offer which would support or contradict this assumption, I'd be grateful for it.
My next assumption is that, across the US, the two regional variants with the largest number of speakers are Puerto Rican Spanish and Mexican Spanish. Does anyone know if that's incorrect, or if it's correct but not the best way of thinking about the issue?
My third assumption is that it's much easier to ascribe specific regional/national variants of Spanish if one breaks the US into bite-sized pieces. The easy guess is that most of the native speakers living in Southern California and, say, New Mexico, are speaking Mexican Spanish. I can't go much further than that, though. Does anyone have actual knowledge, from education or experience, about local concentrations of specific kinds of Spanish? For instance, I have the vague impression that there is or used to be a higher concentration of Puerto Rican Spanish-speakers living in the New York City area. Stereotype with no basis in reality? True 40 years ago but not any more? Still true, but more complicated than that?
Most of all, what I really want to know is, how do I find out this kind of thing? I mean, aside from asking on linguaphiles. *
The most pragmatic question for me is, what kind of Spanish is spoken most in eastern Massachusetts/Boston, but my curiosity is a lot more far-ranging than that.
Thanks in advance for any and all information, or advice on how to answer my own questions. I have a feeling I'm missing some pretty obvious things. (The most obvious is - talk to the people in question. But I'm still learning how to say, "How's the weather," and am not up to browsing in Spanish-primary corner stores to get a sense of what kind of Spanish I'm hearing around me. In a few years, maybe, but not yet.)
* ETA: The first person to comment has answered this question with "read a book." Actual references to any sources - print, internet, or other - you have found to be up-to-date, unbiased and informative would be entirely welcome.
EATA: In response to the wishes expressed in the first comment, I have edited this post significantly to try to make it more concise and focused. I apologize to anyone who started responding to a version of this post which no longer exists.