Extreme-pedantic nitpick: Jersey is not, strictly, in the UK. The Channel Islands, which include Jersey, are British Crown Territories, and not part of the United Kingdom of Great Britain and Northern Ireland. However, as the point at issue seems to be distances between territory which counts as “France”, and parts of the British Commonwealth – Jersey’s precise status would appear, here, to be moot.
If the Channel Islands / France matter is to be embarked on; by my reckoning, the shortest distance in that category is in fact from another Channel Island – Alderney – to the French (Normandy) mainland: about 10 miles.
If former geographical boundaries can be considered, how far from the main part of post-World War I Germany was the nearest part of East Prussia (with Danzig/Gdansk in between)?
This is not exactly what the OP is looking for, but still a fun fact: the tiny islet of Märket (about 100 m across) in the Baltic Sea on the Swedish/Finnish border has an extraordinary border geometry, which would make it theoretically possible for a thrower with a good, strong arm to make a straight throw from country A *across country B and country A *to finally land in country B!
I don’t know if it has ever been done, but I bet some athletic Finn (a people known to casually throw the javelin 70 m or so) on a sailing vacation has made it, even if there is no official record of it.
Are there other places in the world where this could be pulled off?
Baarle-Hertog and Baarle-Nassau would seem to have that. In fact you could probably add another crossing and land back in country A in a section not connected to the part you threw from. Looking at the map, while it doesn’t have a scale, I’m guessing you could throw from segment H5, across a thin strip of Netherlands, a strip of H1, another strip of Netherlands, and then land in H1. However, such a throw may be only theoretical. It’s a town, so buildings may preclude actually doing it.
There’s a distinction here that is both technical as well as politically significant. Places like French Guiana and Alaska are considered integral parts of the countries that they belong to, despite being “disconnected” physically in some way. Places like the US Virgin Islands, British Virgin Islands, and many (but not all) “overseas” archipelagos are considered external territories - they are under the rule of the country that they belong to, but are not considered fully part of it. For many of these external territories, their political status is not very important on a day-to-day basis and people hop back and forth between the territory and the country proper all the time with little hassle. The territorial status can be important when it comes to voting and taxes, but otherwise it is more of an academic exercise.
This is interesting - Angle Township Minnesota. The only way to get to it is to cross a lake, or go through Canada. Apparently it was a mapping error back in 1783.
Myanmar juts far into Tak province in northern Thailand, cutting it almost in two. Phop Phra and Umphang districts do touch each other, but most of the time it’s much easier just to cut through Myanmar, which I believe many people do. Probably less dangerous nowadays than it used to be. You can see it in this map. Myanmar is on the left, while Phop Phra district is #7 and Umphang #8.
I find a good deal about the Thailand / Myanmar border – indeed the general geography of the whole region, with the very long, thin Isthmus of Kra which at last ends up broadening out to become Malaysia – quite diverting. Not far south of the mentioned Phop Phra and Umphang, Myanmar gets very “slim” for a little while – with Thai territory less than 50km away from the Andaman Sea. The narrow bit of Myanmar called Tenasserim goes on for hundreds of kilometres southward, along the west coast of the isthmus, making Thailand in turn decidedly “thin”: only some 20km wide at one point, if I’m measuring correctly !
