Walking distance to me is about a half-mile -- 10 minutes at normal human walking speed. Some subjective factors weigh in as well, such as how pleasant the walk is, and what you see along the way. Most people would rather walk for 10 minutes along Holland Street than 5 minutes on McGrath Highway.

Porter Square Shaw's is about a 10 minute walk in the other direction.

Somerville has a citywide height limit of 4 stories or 50 feet. The Teele Square development doesn't violate this, but the original proposal for One Davis Square would have.