What's the talk about Boston being similar in size as Philly?

Sure, Boston has 5.8 million people in its CMSA but that doesn't mean much, only commuting patterns. If you look at urbanized area population, Philadelphia is significantly larger and is denser as well. Philadelphia (4th largest urbanized area) 5,149,079 in 1,799.51 sq. miles and a density of 2,861.4 ppsm. Boston (7th largest urbanized area) 4,032,484 in 1,736.18 sq. miles and a density of 2,322.6 ppsm. When it comes to size, Philadelphia is larger by a clear margin.>