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First, It is a bit difficult to understand the concern without knowing the type of site at least: is it a retail site keeping the single website and just including the new location? A service business? A restaurant? What is size of the site? Assuming that you already have set up the Places, Bing Business Portal, and Yahoo Local in NY, and that you understand you are going to maximize those listings as you did in Miami: pictures, videos, city mentions, reviews pertinent to NY as opposed to Miami, etc., the next thing is how to market your search terms within New York. You mention optimizing New York terms without compromising Miami, is there a way to have other content pages that use New York but are not duplicate to Miami? Again, a bit more info would help.