So the Trulia study concluded that 100% of Bostonians consider themselves living in an urban environment. The authors admit they couldn't survey people in every city - they interviewed 2,008 people while there are more than 30,000 ZIP Codes - so they hypothesized. From what I understand, they took the number of 2,213 residents per square mile as the dividing line. If a neighborhood - which to them was a ZIP Code - had more than that number it was urban, less and it was suburban, with some other undefined criteria. West Roxbury, Roslindale, and Hyde Park, which I consider "suburban" have density above that benchmark, Hyde Park the lowest of the 3 with around 5,300 ppsm.