I always prefer to avoid acronyms wherever possible in the tags, but united states of america would be an unwieldy tag for the amount that it gets used. Here the acronym makes sense.

I tag all UK posts with united kingdom followed by a separate scotland.edinburgh tag. This is more to do with sensitivity to the issue of governance among the residents of these regions under the UK umbrella, rather than following a rigid rule such as united kingdom.scotland.edinburgh. Plus personal preference, I try to avoid double dots in any tags wherever I can.

The tags should be more organic in my eyes, more instinctive to implement for first time users, rather than getting bogged down in the mire that can be the Dewey decimal style classification.

Tags and hierarchy are two topics that get discussed every now and then (along with groups and subgroups). Since Tildes is still in early development, I am not certain if there are strict standards implemented yet (nor do I think there should be). I do however trust that the ones most familiar with Tildes development are aware of those topics and working towards that end.

Related topics:

• Guidelines for tagging country topics that users generally try to follow
• Geographical tags
  This topic in particular appears to show that in some cases acronyms/abbreviations are preferred, such as on mobile devices or for brevity. While other times less ambiguity is preferred.
• Is there any progress on tag synonyms?

GitLab issues that I think apply:

• Add topic tag synonyms from Topic Tagging doc page submitted by haykam
• Add the ability to define synonymous topic tags for use in the tag autocomplete feature, so that the more prevalent version of those synonymous tags will still show up as a recommendation submitted by cfabbro
• Handling multiple nested topic tags with common parent tags submitted by Cassidy Dingenskirchen
• Add interface for bulk editing tags. submitted by cfabbro