It's fascinating to see how some of the main constructs that help define a city ie. major roads, intersections, are still highly visible and intact over 100 years later.
Would recommend "The City in History" by Lewis Mumford. Great read about how cities have formed, died, and some renewed throughout history.
Fascinating, but probably shouldn't be surprising. By 1860, Boston was already 1/3 of it present size--too developed for wholesale re-layouts to happen without something major (like the Great Chicago fire did in Chicago).
Look at this map of lower Manhattan from the 1600's to today: http://www.racontrs.com/stories/nyc-land-reclamation. Look how, aside from land reclamation, the basic street architecture has changed little since the mid 1700's.
Would recommend "The City in History" by Lewis Mumford. Great read about how cities have formed, died, and some renewed throughout history.