<div dir="ltr"><div class="gmail_default" style="font-size:large">Thank you for the response. Yes I agree that some "handwork" could be used here but I think I should pursue the automated solution until I cannot implement it. I have found that the using the census data does indeed find counties where the coordinates indicate isolation, so my plan to focus on isolated counties is what I am pursuing at the moment.</div><div class="gmail_default" style="font-size:large"><br></div><div class="gmail_default" style="font-size:large">However, I found that the census data does not provide a consistent identification of isolated counties across states. There is a huge difference between Masachuchetts and Washington states. The census data does identify Dukes County as isolated but does not identify San Juan County as isolated. In fact, San Juan county is connected to Whatcom and Skagit Counties but does not identify San Juan County as connected to Island, Clallam and Jefferson Counties, which are clearly neighbors even though a little further away. Dukes County and San Juan Counties have roughly the same distance to the nearest county, so there must be some distance parameter at work when the dataset was created, but this theoretical parameter seems to implemented differently in these two states.</div><div class="gmail_default" style="font-size:large"><br></div><div class="gmail_default" style="font-size:large">This finding complicates the algorithm I dream about refining.</div><div class="gmail_default" style="font-size:large"><br></div><div class="gmail_default" style="font-size:large">BTW: The coordinate files from xxx.yyy say that San Juan County has five neighbors {Whatcom, Skagit, Island, Clallam and Jefferson Counties}. This result seems correct to me geven the goals of the project. Similarly, xxx.yyy identifies Dukes County as having mainland counties as neighbors.</div><div class="gmail_default" style="font-size:large"><br></div><div class="gmail_default" style="font-size:large">I have attached maps for reference.</div><div class="gmail_default" style="font-size:large"><span style="font-size:small"></span></div><div class="gmail_default" style="font-size:large"><br></div><div class="gmail_default" style="font-size:large"> </div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Mar 10, 2026 at 3:43 PM David Strip <<a href="mailto:qgis-user@stripfamily.net" target="_blank">qgis-user@stripfamily.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
<div>
If you are determined to have an automated method, you can find
neighbors using <a href="https://gis.stackexchange.com/a/418824/4449" target="_blank">this approach.</a><br>
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. <br>
<br>
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:
<blockquote>
<div>
<div>
<h2>1. <span>Hawaii (All 5 Counties)</span></h2>
<p>As the only state located entirely on
an archipelago, all its counties are island-based.</p>
<ul>
<li>
<p><b>Hawaii County:</b> The "Big
Island."</p>
</li>
<li>
<p><b>Honolulu County:</b> Oahu and
the Northwestern Hawaiian Islands.</p>
</li>
<li>
<p><b>Kalawao County:</b> A small
peninsula on Molokai (the smallest county in the US).</p>
</li>
<li>
<p><b>Kauai County:</b> Kauai,
Niihau, and others.</p>
</li>
<li>
<p><b>Maui County:</b> Maui, Lanai,
Molokai, and Kahoolawe.</p>
</li>
</ul>
<h2>2. Washington (2 Counties)</h2>
<p>While most of Washington is on the
mainland, its northwestern corner is home to:</p>
<ul>
<li>
<p><b>Island County:</b> Comprised
primarily of Whidbey and Camano Islands.</p>
</li>
<li>
<p><b>San Juan County:</b> Comprised
of the 170+ islands that make up the San Juan
archipelago.</p>
</li>
</ul>
<h2>3. Massachusetts (2 Counties)</h2>
<ul>
<li>
<p><b>Nantucket County:</b>
Coextensive with Nantucket Island and its tiny neighbors
(Tuckernuck and Muskeget).</p>
</li>
<li>
<p><b>Dukes County:</b> Comprised of
Martha's Vineyard and the Elizabeth Islands.</p>
</li>
</ul>
<h2>4. New York (2 Counties)</h2>
<p>Technically, two of New York City's
boroughs are their own island counties:</p>
<ul>
<li>
<p><b>Richmond
County (Staten Island):</b> Comprised of Staten Island
and surrounding smaller islets.</p>
</li>
<li>
<p><b>New
York County (Manhattan):</b> Comprised of Manhattan
Island, Roosevelt Island, and others. (Note: A tiny 0.1
sq mile neighborhood called <b>Marble
Hill</b> is physically on the mainland due to a canal
being dug in 1895, but it remains legally part of the
island county).</p>
</li>
</ul>
<h2>5. Rhode Island (1 County)</h2>
<ul>
<li>
<p><b>Newport
County:</b> While some of its towns are on the
mainland, the county itself is largely defined by <b>Aquidneck
Island</b>, <b>Conanicut Island</b>, and <b>Prudence
Island</b>. 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.</p>
</li>
</ul>
<h2>6. Florida (1 County*)</h2>
<ul>
<li>
<p><b>Monroe
County:</b> This is a "hybrid" case. While the
populated <b>Florida Keys</b> are entirely
islands, the county boundaries actually extend onto the
mainland to include a large, uninhabited portion of the
Everglades.</p>
</li>
</ul>
</div>
</div>
<br>
</blockquote>
</div>
</blockquote></div><div><br clear="all"></div><div><br></div><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr">Brent A. Blumenstein, PhD<br>Trial Architecture Consulting<font color="#000000"><br><span style="background-color:rgb(255,255,0)">Port Saint Lucie Florida USA</span><br></font><a href="http://www.TriArcConsulting.com" target="_blank">www.TriArcConsulting.com</a><br>bab@TriArcConsulting.com<br>mobile: +1 (206) 390-0081</div></div></div></div></div></div></div></div></div></div></div></div></div></div>