David, Brent and list, On Tue, Mar 10, 2026 at 12:43 PM David Strip via QGIS-User < [email protected]> wrote:
> If you are determined to have an automated method, you can find neighbors > using this approach. <https://gis.stackexchange.com/a/418824/4449> > Then look for counties with no neighbors. For these counties look for the > closest counties in the same state and add these to the list. > Disclaimer - not from the USA so my opinions here may not count. Having said that, I'm not comfortable with the exhaustiveness of David's proposal below. > > But that seems like a lot of work for a small problem. A cursory search > suggests the number of island counties is quite small and you can patch up > the data by hand: > > 1. Hawaii (All 5 Counties) > > As the only state located entirely on an archipelago, all its counties are > island-based. > > - > > *Hawaii County:* The "Big Island." > - > > *Honolulu County:* Oahu and the Northwestern Hawaiian Islands. > - > > *Kalawao County:* A small peninsula on Molokai (the smallest county in > the US). > - > > *Kauai County:* Kauai, Niihau, and others. > - > > *Maui County:* Maui, Lanai, Molokai, and Kahoolawe. > > 2. Washington (2 Counties) > > While most of Washington is on the mainland, its northwestern corner is > home to: > > - > > *Island County:* Comprised primarily of Whidbey and Camano Islands. > - > > *San Juan County:* Comprised of the 170+ islands that make up the San > Juan archipelago. > > 3. Massachusetts (2 Counties) > > - > > *Nantucket County:* Coextensive with Nantucket Island and its tiny > neighbors (Tuckernuck and Muskeget). > - > > *Dukes County:* Comprised of Martha's Vineyard and the Elizabeth > Islands. > > 4. New York (2 Counties) > > Technically, two of New York City's boroughs are their own island counties: > > - > > *Richmond County (Staten Island):* Comprised of Staten Island and > surrounding smaller islets. > - > > *New York County (Manhattan):* Comprised of Manhattan Island, > Roosevelt Island, and others. (Note: A tiny 0.1 sq mile neighborhood > called *Marble > Hill* is physically on the mainland due to a canal being dug in 1895, > but it remains legally part of the island county). > > 5. Rhode Island (1 County) > > - > > *Newport County:* While some of its towns are on the mainland, the > county itself is largely defined by *Aquidneck Island*, *Conanicut > Island*, and *Prudence Island*. However, it is often excluded from > "entirely island" lists because a portion of the county (the town of Little > Compton and Tiverton) is physically attached to the Massachusetts mainland. > > 6. Florida (1 County*) > > - > > *Monroe County:* This is a "hybrid" case. While the populated *Florida > Keys* are entirely islands, the county boundaries actually extend onto > the mainland to include a large, uninhabited portion of the Everglades. > > I'm assuming that there are more than one island in the USA that contains more than one county; certainly Long Island incorporates four counties: Nassau, Suffolk, Queens and Kings. As well, Queens and Kings are also boroughs of New York City. Given what I understand of Brent's interest, it seems to me that there is a kind of "adjacency" relationship between Queens, Kings (Brooklyn) and Manhattan, Bronx and Richmond counties, that is, the boroughs of New York City. I don't know if Brent would consider Nassau and Suffolk counties to be "adjacent" to Manhattan... Also there is the question of adjacency across state lines, I suppose... For example, Long Island looks pretty adjacent to Connecticut to me. Does that count? -- Chris Hermansen · clhermansen "at" gmail "dot" com C'est ma façon de parler.
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