Are you speaking of communities and regions within the United States specifically?
If so, one must recognize the ever-moving nature of people within the American anarchist scene. It is not often that I have come across an anarchist community in any town that is comprised entirely of people /from/ that town or region. People move and gravitate towards groups of people that share similar ideas, areas that offer resources they desire. So, if one were super into Queer Insurrectionism one may gravitate more towards the Midwest, because that is where groups such as Bash Back! have been popular. Or if one were anti-civilization/primitivist one may be drawn more towards the Northwest rather than, say, New York City, because of the more natural environment and in the process create a community that leans towards "green" anarchism.
People go where they fit in, they look for commonality - it really is as simple as that.