The sharing economy is transformative in that it decentralizes services by permitting direct transactions between individuals. A less recognized consequence is that it also decentralizes the geography of services, shifting their distribution away from major business districts and into residential communities. We present a three-part generalized theory for studying and developing policy responses to the arrival of these services in neighborhoods where they were not previously available. First, one must quantify the distribution of the new services across neighborhoods. Second, these geographic shifts in supply and demand can generate positive and negative externalities for communities, which might be hypothesized and tested for empirically. Third, policy responses can be developed based on the knowledge generated by components 1 and 2. We illustrate this proposed theory by examining the incursion of Airbnb short-term rentals into the neighborhoods of Boston, MA for 2010 to 2018. We demonstrate that Airbnb listings quickly grew into neighborhoods away from the downtown core where hotels are concentrated and hypothesize how this might increase investment in local buildings (measured through building permits), activity at local food establishments (measured through the number of new licenses), and crime (measured through 911 reports). We find initial evidence for increased investment through building permits and limited evidence for increased violent crime, but no evidence for increases in food establishments. This can then guide how cities regulate short-term rentals to maximize benefits and minimize negative impacts. We conclude by exploring how the theory might be applied to other forms of the sharing economy.