A central definition considers the six New England states—Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont—as the Northeast, due to their closely related histories, cultures, economies, and dialects.
Some include the three contiguous Mid-Atlantic states—New York, Pennsylvania, and New Jersey—because they share some of these factors, are part of the Boston–Washington megalopolis, and have economic and cultural ties to New England. The three have also been historically viewed as part of New England.
Definitions often include Maryland and Delaware, which lie south of the Mason–Dixon line, because of their close historic, economic, and cultural ties to Pennsylvania and New Jersey, as well as the large proportion of their populations born in those two states.
The inclusion or exclusion of these five Mid-Atlantic states in definitions of the Northeast has led to a narrower and a broader definition: the narrower definition includes only New England; the broader definition includes all nine of these states.
Some sources further include West Virginia, which is closely tied to the broader Northeast in some ways, including significant migration and cultural ties to the region. However, West Virginia is usually considered a part of the South, Appalachia, or Mid-Atlantic region.
As an international region, the Northeastern United States is the most economically powerful and heavily populated one of the developed countries outside of the EU, with a GDP of over $5.5 trillion (about 18.5% of the total US economy) and a population of over 56 million.
The Northeastern US contains four out of the ten most populous urban centers in the nation: Greater New York City (with over 20 million), Philadelphia (with over 6 million), Boston (with over 4.5 million), and Washington, D.C. (with over 6 million).
The Northeast has a higher population density (370 people per square mile) and urbanization rate (over 85%) than the national average. The megalopolises of the Northeastern United States are part of the Northeast Megalopolis, which stretches along the Atlantic coast from Boston to Washington, D.C.
