Decision logic first
Transit-visa checks usually come down to four things: your passport, the airport, whether you enter the country, and the ticket / baggage setup. Different airports in the same country can still have different airside-transit rules. If you must collect and re-check baggage, that often raises the chance that entry rules apply. Separate tickets and longer layovers usually deserve another review. Airline, airport and immigration rules shift quickly, so re-check before booking. Common high-intent questions
Does a Chinese passport need a transit visa via Canada?
Does an Indian passport need authorization for a UK connection without leaving the airport?
How do through tickets vs separate tickets change Schengen transit checks for a Philippine passport?
Does a Vietnamese passport always need a valid U.S. visa to transit in the United States?