I do not believe Boston has lost population over the last 20 years. Boston had 562000 people in 1980 and 574000 people in 1990 according to the US census. The 2007 Massachusetts census showed 599000.
Also NYC has about 14 times the population of Boston, so if Boston creates 2000 housing units and NYC creates 35000 in a year, that isn't a very big discrepancy proportionately--it would be like Boston creating 2400 housing units.
Bookmarks