I would argue that using the states/provinces should be the standard, not the exception or "eliminated".
I would argue that the more important thing at the USA/CAN or USA/MEX border is that it's an international border. It's more relevant information than it being the MN/MB or whatever.
A total I-5 clinch, for instance, is between the Mexican and Canadian borders, not between two BC borders!
It shouldn't be I-5 CA BC/CA WA WA/BC. It should be I-5 CA MEX/USA WA USA/CAN.
Si404 - Is it correct that all other continents use country codes?
Actually, looking, I've found an exception on the Franco-Dutch border (which is bizarre as no one would ever call it the Saint-Martin / Sint Maarten border). Though that's in North America, so isn't 'other continents'
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But yes. Ever since that Ur example (which is the inter-country border in the world most likely to be referred to as Country/Region rather than Country/Country) countries has been what's been used by me, even when countries are subdivided (internal borders obviously use province/state/whatever codes) - as is the case in that original example (GBR rather than NIR).
Also that significant work to change them if true.
Very true. As well as most North American border points, every French, Spanish and German border point would be divergent from that standard - or at least the ones on their shared borders: if one side is a country, should we have the mismatch?
I think anything like ND/Can needs to be changed due to being neither one thing nor the other. 'Can' rather than 'CAN' is clearly odd, but also inconsistency with what the border is: ND/CAN is still not right because Canada is split just like the USA. Whether that's ND/SK or USA/CAN is a different question, but I've given my answer above in favour of countries.
But it's a bit different with borders of multi-region countries and single-region countries. You could possibly make the case for OCC/CT (Occitan/Catalonia) for the FRA/ESP (France/Spain) border points at the eastern end of that border - I think it's hard, but... But is it OCC/AND and AND/CT for the Andorran borders? Is it the Oder the Brandenburg-Poland border, or the German-Poland border? The latter seems better.