When a visitor enters a community, he or she can easily observe some outstanding social norms as far as the way people behave towards each other. This can tell the visitor about the general morals, values, and outlook of the general population. However, there will always be people in a community who are the exception to the rule.
Norms are unwritten rules that a group of people follow without question. If one person deviates from the rules than he or she is not accepted. Every community has its own set of norms, even if they are not aware of them. You can tell a lot about a community by what they do and do not belive in and accept.
Yes, local norms can give a comprehensive overview of a community, because local norms are what most people do. From what is common we can figure out what common values most of the people in the area usually do. Although it might not apply to every person, it is a way to figure out common culture.
I do not believe local norms can give a comprehensive overview of a community. I can use Nashville as an example. Someone who wants to follow local norms may think it is smart to develop an accent. The truth however, is the fact that only a small percentage in the area actually have an accent. There are so many people there that have relocated that the population is very diverse. For this reason, local norms do not give a comprehensive overview of a community.