Why is 台北 spelled Taipei, not Taibei? I just tried to type in taipei in iOS but it didn't return any correct prediction. After my investigation, I found that it is taibei, not taipei, to get the correct pinyin result.

However, now I wonder why it is called taipei. 台 is tai like 台风 and 北 is bei like 北美洲. So why is it called taipei? I think in traditional chiese it should also be typed in as taibei...
From wiki: the spelling "Taipei" derives from the Wade–Giles romanization T'ai-pei. "Taibei" is pinyin, which iOS supports as an input method.

Wade-Giles used to be the standard method of romanization so it shows up in a lot of older Chinese names like "Chiang Ching-kuo".

Pinyin has its own disadvantages, especially when spoken by English speakers. Consonants like "zh", "q", or syllables like "ri", "shi" sound very different from what an English speaker might expect.