According to a ranking produced by the Henley Passport Index which collected date from the International Air Transport Association, Japan holds this year's most powerful passport in the world for a fourth year in a row now. How is the ranking measured?The ranking is based on the amount of countries a passport holder can enter without needing a visa or with the ability to obtain a visa immediately upon arrival. Japanese passport holders can currently visit 191 countries without needing a visa, solidifying its position as the the strongest passport in the world. The Singaporean passport remains at number two again this year with the ability to visit 190 countries visa-free. Surprisingly, Brexit has actually helped the British passport in becoming stronger by moving one ranking up from last year's number eight position. This year, it is tied at the number seventh spot with Belgium, New Zealand, Norway and the US with a total of 185 destinations that can be travelled to without needing a specific visa. Asian countries are increasingly dominatingThe HPI explains that, in more recent years, Asia Pacific countries have dominated the top spots of the ranking:Over the index’s 16-year history, the top spots were traditionally held by EU countries, the UK, or the US, and experts suggest that the Apac region’s position of strength will continue as it includes some of the first countries to begin the process of recovering from the pandemic.Interestingly, over the past seven years, the American passport has lost strength and has dropped from the first position to the seventh. And as for the world's least powerful passports? Afghanistan, similar to last year's ranking, is currently the weakest with its citizens being allowed to visit a mere 26 countries without needing a visa.