If you removed the official boundaries, Boston and its surrounding inner suburbs (some of which happen to be denser than Boston itself) are clearly one singular city. There is no visual break between the buildup. It's all the same big urban area. It's all one city and can't be separate out from a build-up perspective. It all feeds into itself. None of the inner 'burbs are self-sustaining on their own, particularly Somerville. There is no gap of non-urban space between the boundaries. It's all clearly one big city that happens to have multiple boundaries for political purposes.