> Somerville considering it's in the top 10 most dense cities in the US

I would believe that Somerville is the most dense from a "number of residential properties per unit area" standpoint. But when each of those properties contain only 3 to 5 people living in them each, the actual population density isn't going to be crazy high. Compare Somerville to places that have a lot of multistory condominiums (with hundreds of people living in them each) from a "number of people per unit area" measurement... and the Condo's will blow Somerville out of the water from a population density standpoint