Having lived in Boston for around 30 years, I've noticed now and then that many people there are confused about what a city is. Since every two-bit hamlet in New England that has outgrown the "town meeting" system of government sees fit to call itself a city, this is understandable.
city, n.: a more-or-less contiguous region served by a 24-hour public transit system and possessing at least one walkable district containing 24-hour restaurants, food markets, bars, and coffee shops
New York, London, Tokyo; Chicago, Seattle, even (as I'm discovering) New Orleans: these are cities; Boston, by contrast, is an agglomeration of college towns. Boston hasn't yet even managed to annex most of its major neighborhoods: if it were a city, Brookline, Cambridge, and Somerville would all be part of it for sure, as probably would Malden, Revere, Arlington, Medford, Dedham, Chelsea, Waltham, and so on. As it is, not a single subway line stays within the "city".
Since Boston has abdicated its seemingly natural leadership role in the region, there is something of a power vacuum crying to be filled. Of the various neighborhoods served by subway lines and calling themselves "city", I continue to believe that Somerville has the strongest natural claim, not least because we are free of major ties to any of the local degree-granting institutions, allowing us to act as a neutral arbiter rather than a captive government like our neighbors to the north and south. Write to your mayor, councillor, or selectbeing today and tell them you want to merge with Somerville.