BOSTON ISN’T MAKING land anymore. Despite our best efforts—filling in the Back Bay, Seaport, and much of the harbor—we now must finally face the question of not only where to build, but also whether we have space to build at all. Choosing between hospitals and housing, stores and schools, building in Boston has become a zero-sum game where some interests win and others lose. These trade-offs were on full display earlier this year when the Boston…