A border portmanteau is a region or town near a mutual border that combines the names of two, or occasionally three, adjacent states. The most famous example is probably “Texarkana” which is a combination of Texas, Arkansas and Louisiana. There is a Texarkana, TX and a Texarkana, AR. Having seen “Pen Mar, MD” on the map, I was curious as to which state borders have a border portmanteau.
I generated the border geometries using a slightly modified version of the adjacency code described here. The data came from the “Border portmanteaus” section of the List of geographic portmanteaus Wikipedia article. Some border portmanteaus no longer exist (ex. Nosodak, ND) or have no current population (Oklarado, CO) but are included anyway.
Nice