Choose the guide by the trip signal
The hotel base and daily movement matter more than the wider route.
Regional sequence and transport choice come before city detail.
Do not force one guide to answer decisions owned by another place.
Use city guides for city-base trips
Open Boston Guide, Providence Guide, or New York City Guide when the trip is already centered on that city and the next decision is where to stay, eat, arrive, and spend the first day.
Use statewide guides when the route is still open
Open Massachusetts Guide, Connecticut Guide, Rhode Island Guide, or New York Guide when you are comparing several places, pairing coast and city, or deciding whether the trip needs a car, train, ferry, or different base.
Let nearby borders shape the handoff
A Mystic or Stonington plan may belong in Connecticut even if it starts from Rhode Island. A Hudson Valley or Long Island plan may belong in New York even if the first night is in New York City.
Separate arrival convenience from trip identity
A flight or train station may determine the first night without defining the whole trip. Use the city guide to protect the arrival, then hand the remaining nights to the state guide if the real purpose is a coast, campus town, island, valley, or mountain region. This prevents a convenient gateway from becoming an unnecessarily expensive or inconvenient base for every day.
Keep one primary question per guide
Boston Guide should answer Boston-base questions; Massachusetts Guide should compare the rest of the state. Providence Guide should finish a Providence weekend; Rhode Island Guide should compare Providence with Newport, South County, Block Island, and other statewide choices. New York City Guide owns the city; New York Guide owns the corridors beyond it. That boundary is what makes the network useful.
Build the handoff around the overnight change
A second guide earns a place in the plan when the overnight base, transport mode, or dominant daily geography changes. A day trip does not automatically need a second planning system; a new base usually does. Mark the handoff day explicitly, protect the transfer, and let each guide own the nights on its side. The result is a Northeast itinerary with fewer repeated crossings and clearer booking decisions.