The people of Bangor Maine and Buffalo NY have a hell of a lot more in common with the people of Cincinnati Ohio than they do with the people of Portland Maine and NYC.
On the west coast the "wealthy urban and suburban areas on the coast" vs "literally everywhere else" difference is even more stark. And I'm not talking about just the urban vs rural divide. The people of secondary cities resent being ruled by the interests of the major metropolitan areas as much as the rural folks do.
Cities/MSAs are the drivers of cultural identification in America, much less so than states.
Nearly 100% of Michigan is 150 miles or less from an international border that is in navigable waters. Is it a coastal state?
Navigable Waters of the United States has a specific legal definition [1] and it has nothing to do with whether it's salt water or fresh water. So the question of whether a particular state is "coastal" based on proximity to salt water a valid question!
Counties have a variety of shapes and sizes, so that doesn't really tell you proximity to the coast, but a majority of the population lives within 50 miles of the coasts.
[1] Let's say a day's drive is around 400 miles, since if you go north traffic is rough.
DC - Maryland - Virginia
aka "The greater Washington, DC metro area"
My general cut of it would be Frederick - Leesburg - (follow US 15 south) - Gainsville - Quantico - La Plata - Waldorf - Bowie - Laurel - back to Frederick, although I'm not high confidence of the cuts on the MD side of the line.
An additional factor to consider in the DC area is that the DC central business district is relatively weak compared to other major jobs centers: Arlington, VA (just across the river) has hefty job concentration, as does the Dulles-Tysons corridor; on the MD side, there's an additional jobs concentration on Rockville-Bethesda.
The final factor is of course the Baltimore-Washington divide. As you head northwest in MD, more people start commuting to Baltimore instead of Washington. So instead of there being a relatively clean sprawl/rural divide you can point to as a boundary, there is instead a more or less continuous sprawl that transitions from DC suburbs to Baltimore suburbs, and the mixing zone (particularly the Laurel-Columbia belt) is more accurately a suburb of both rather than one or the other.
Maryland also did a better job of spreading out its employers. A lot of those Virginia exurbs still commute into DC, or at least Northern Virginia, making traffic a nightmare, at least during rush hour.
Another thing that slightly confuses that map: Virginia has much better arteries into DC. You get into DC from the south on I-395 and I-66, and they take you all the way downtown. Maryland has only surface streets. (It was supposed to have I-95 connecting straight through the city to join up with I-395, and I-595 where New York Avenue is, but that would have destroyed a lot of neighborhoods in exactly the way they were destroyed in building 66 and 395.)
That means that there's a fair bit of Virginia that is technically 45 minutes away from the center of the city, but not during rush hour. The 45 minute line in Maryland is pretty close in, but the 1 hour line turns out to be quite broad, because you can reach it on Maryland's interstates that flow pretty freely (parts of it, even during rush hour).
Of course you really should be taking public transport, except during a pandemic. The driving and parking are both horrible.