The map of what America has become in JMG’s Star’s Reach is based on his answer about the ocean level rise in that era:
Peakfuture, the sea level rise in Star’s Reach is 50 meters. You might also consider putting in the new national borders: Meriga extends from the Appalachians to the Missouri River; Nuwinga is the current New England; Genda is Ontario, Quebec, and the Maritimes; the Coastal Allegiancies extend down the eastern seaboard from Maryland south to where Florida used to be, up to the Appalachian crest; the Meycan empire has expanded into California, Texas, and those other parts of the Southwest that aren’t completely uninhabited; there’s an empty zone extending between the Rockies and the Sierras and Cascade ranges, which is as dry as the Sahara and a lot more polluted, and nobody lives there; and then there’s the Neeonjin country, which runs along the coast from far northern California up to the Alaskan panhandle, and is inhabited by the descendents of Japanese boat people.
So, the map of the Star’s Reach world looks approximately like this, as far as I can tell.
Between the Missouri and the Rockies, things may be a bit dicey, as the Ogallala aquifier, a main source of agricultural water will most likely be gone by that time. The black line on the map is the approximate ridge line of the Rockies, so the Empty Zone might extend more to the east of that line, as shown by the dotted line.
Of course, things are going go be a lot more fluid, with a lot less straight lines. For example, Nuwinga may not run in a straight line down the old man-made New York border, but the flooding of the Hudson, Lake George and Lake Champlain will give a more defined border set by Nature. Note how Boston is completely gone; my bet is the city of Worcester, or some other city on the Connecticut river will become the capital, but cities like Hartford are only 50 feet above sea level. It is tough to predict things, but given that sea level rise will start to take chunks out of Boston slowly, people might move to places as close as can be. Also, if state governments are still functioning, they’ll want to remain in the state, and that might be a natural new capital for Massachusetts, as it once was connected to Boston and Providence via canals (again!).