This question was recently closed as "too broad" and/or because of the strong chance answers might be based on experience. The question seeks factual information, not subjective opinions. The second paragraph gives very specific criteria and the third paragraph further spells out intended uses that provides another specifying test for what answers would be considered addressing the question (i.e. if the answer could serve the purpose of that knowledge spelled out there). Answers would be in the form of probably-small sets of cities each with short explanation, not something that would be too long for this format.
In comparison, this question ("Which European cities are connected by convenient night boat?") also focuses on transit and seeks answers in a similar format. It's considered a Good Question, rewarded with a silver badge, and after a chat discussion concluding it was not too broad, was even criticized for not being broad enough because it didn't ask about trains as well as boats.
Recent chat indicates that what counts as "too broad" is changing from what it used to mean, so here's a meta question to ask/discuss what are "today's rules" about what's "too broad?"
If there is a decision rule being applied, are there pros and cons that would guide a decision on if it's the rule we should be applying? Does it distinguish between the two questions discussed in the first two paragraphs of this question (and if so, how)?
The answers to this meta question should be helpful for addressing questions like this recent one, and would be helpful for folks like me to know what can and can't be asked on Travel.SE. Looking at existing well-received questions and help resources is evidently not a sufficient guide, but a meta discussion on this specific point should be.
