Success! On Wed, Mar 11, 2026 at 11:45 AM Brent Blumenstein <[email protected]> wrote:
> Thanks - I will explore immediately. Seems like I chose the wrong file > based on ignorance, which is not an uncommon event. > > On Wed, Mar 11, 2026 at 10:21 AM Keith Jenkins via QGIS-User < > [email protected]> wrote: > >> Hi, Brent. >> >> In your original message, you mentioned the cb_2020_us_all_500k.zip >> boundaries, which are clipped to the shoreline. >> >> You might also be interested in looking at the Tiger/Line shapefiles >> that are available here: >> https://www.census.gov/cgi-bin/geo/shapefiles/index.php >> >> These boundaries are not clipped to the shoreline, so the polygons for >> counties like San Juan and Whatcom extend out into the water and >> actually share a border, and thus are truly adjacent polygons. I'm >> attaching a map image to illustrate -- the thick borders are the >> Tiger/Line shapefiles. >> >> The US Census Bureau also publishes a county adjacency file which I >> think is based on the Tiger/Line polygons. >> >> https://www.census.gov/geographies/reference-files/time-series/geo/county-adjacency.html >> >> Keith >> >> >> On Wed, Mar 11, 2026 at 3:18 AM Brent Blumenstein via QGIS-User >> <[email protected]> wrote: >> > >> > 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. >> > >> > 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. >> > >> > This finding complicates the algorithm I dream about refining. >> > >> > 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. >> > >> > I have attached maps for reference. >> _______________________________________________ >> QGIS-User mailing list >> [email protected] >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user >> > > > -- > Brent A. Blumenstein, PhD > Trial Architecture Consulting > Port Saint Lucie Florida USA > www.TriArcConsulting.com > [email protected] > mobile: +1 (206) 390-0081 > -- Brent A. Blumenstein, PhD Trial Architecture Consulting Port Saint Lucie Florida USA www.TriArcConsulting.com [email protected] mobile: +1 (206) 390-0081
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