Today is a holiday in Boston, Evacuation Day, commemorating the date (actually March 17 177) when a fleet of 120 ships carrying British troops departed Boston Harbor, leaving control of the city to the Continental Army.
After the battles of Lexington and Concord almost a year earlier, it was clear that the battle for Boston came next. As the Washington troops began a 10-month long siege, both camps knew that the key to the city was in the surrounding areas: Bunker Hill to the north, Roxbury Hill to the west and Dorchester Heights to the south. The names explicitly refer to the three high points around Boston. The military commanders knew a couple things that any good architect knows:
That the section is often more important than the plan.
That when looking at the plan you need to put it a broader context.
The British already controlled Roxbury, just west of the Boston Neck that was at the time the only land connection to the city. On June 17, the Battle of Bunker Hill gave the British forces control of the high ground on the Charlestown peninsula but left them too exhausted to tackle Dorchester. A tactical victory with disastrous strategic consequences.
It was a matter of time. When the cannons seized by the Continental Army at Fort Ticonderoga reached Dorchester Heights, the British forces in Boston were at shooting range of the newly emplaced American artillery. At that point, the British had little choice but to evacuate.
Again, remember, pay attention to the section (the high ground in this case) and the context. Also, don't confuse tactics with strategy... it may have been what cost the British their American colonies.