One of the answers to Do we need to use the 'Europe' tag even when discussing just one European country? is Good plan. Use "Europe" if the question is really about Europe, the continent, not just something that happens to be in Europe. That answer presently has the most net upvotes, though has not been accepted.
I am not sure how much of a precedent this may or may not be regarding, for example, the tagging of Do I need a transit visa to pass through El Alto International Airport (LPB), La Paz, Bolivia?, presently:
Answered, as it happens, while I was drafting this. The answer applies to all Bolivian airports, though subject to whether or not any specific one has hotel accommodation. At present we don’t know whether La Paz has such a hotel, so while [bolivia] is relevant, given the answer, that may not answer the actual question.
So, there is room (to spare!) to tag this [bolivia] and the answer does cover airports other than La Paz.
On the other hand, the [lpb] excerpt includes “La Paz, Bolivia” so [bolivia] is not helping ‘define’ the question (seems analogous to “Europe” where only one country is concerned.) What are tags, and how should I use them? has A tag is a word or phrase that describes the topic of the question. “Do I need a transit visa to pass through El Alto International Airport (LPB), La Paz, Bolivia?” does not seem to me well described by “Bolivia” with airports, for example, equally ir/relevant.
If [airports] were added (to be consistent with use of [bolivia], then maybe visas (and possibly others) would belong also. At which point there are issues, one of which is only five tags are allowed.
Visa tags are a special case, partly because there are at least 20 of them. Many questions apply more than one of the twenty, sometimes three (possibly more!). For example Is it possible to get a visa on arrival at the airport in Freetown, Sierra Leone? applies visas and visa-on-arrival (no tag for Freetown, Sierra Leone nor for Lungi International Airport).
There is of course another aspect to tagging, also mentioned in the Help Center Tags are a means of connecting experts with questions. It seems quite likely that someone who knows about transit visas in La Paz is more likely an expert on Bolivia than on Indonesian citizens. Or put another way, as a search term, bolivia for the above question does seem useful.
I am sure this has been covered before but my searches of meta have not turned up the guidance I seek. The precedent on SO seems to be that nobody there knows (nor cares).
Tags are added at question time so the person asking can’t be sure that asking about, say, La Paz will receive an answer that applies to all of Bolivia. For describing “the topic of the question” bolivia may be considered positively misleading (far too general) once the geographically much more specific lpb has been applied. (Otherwise why not also/instead international-travel, paperwork etc). Note there are many other examples where different rules apply to different airports in the same country.
So going back to “Europe” and “visas”, I wonder whether the policy is (or if not yet decided, should be) to apply, as relevant, only the most specific of a “family”. If yes, maybe a question such as Visa-on-arrival basics should not be tagged visas. Removing it (and from other questions on the same basis) may impact on the dupe hammer that one user has for the [visas] tag.
Maybe questions should be tagged with as many as possible of the most relevant tags, regardless of the fact that on searching these the hits may vary from highly relevant to at best marginally so. However this will inevitable introduce inconsistency of usage, which conflicts with a classification system being effective. (Similar to the distaste for ‘tag pairing’ where say cambridge is left ambiguous and a separate tag such as [usa] or [uk] is relied upon for differentiation.)
And yet another possibility is to accept that tagging is provisional until answers have been posted.
Where is the guidance on how to apply tags that is specific enough to address handling the conflicts and issues mentioned above?