Several parts combine into one character.

Phonetic-semantic compound: 者 (a phonetic, originally pictographic for "person") + 阝 (the right-side variant of 邑 "town"). The encoded meaning: a town where many people gather = a metropolis / capital. Identical across 繁體 / 新字体 / 简体. Pairs with 京 — where 京 is specifically the imperial seat, 都 is any major city or capital.

Mandarin has TWO tones for 都 — another 破音字, and these TWO meanings are extremely common: — dū (1st tone): capital / metropolis. 首都 (shǒudū, capital), 都市 (dūshì, metropolis), 京都 (Jīngdū, Kyoto in Mandarin pronunciation), 大都市 (dà dūshì, big city). — dōu (1st tone): ALL / both / always (adverb). 我都喜欢 (wǒ dōu xǐhuan, "I like them all"), 大家都来了 (dàjiā dōu láile, "everyone has arrived"), 都是 (dōushì, all are). The 都 (dōu, "all") usage is one of Mandarin's most frequent grammatical adverbs — it appears in nearly every sentence with multiple subjects.

Japanese: on-reading ト (to) is dominant — 京都 (Kyōto, Kyoto, Japan's historic capital), 都市 (toshi, city), 都会 (tokai, big city / urban area), 首都 (shuto, capital city). ツ (tsu) appears in 都合 (tsugō, convenience / circumstances — high-frequency vocabulary). 都合 — meaning "circumstances / availability" — is essential for Japanese scheduling and politeness.

Tokyo Metropolis (東京都 Tōkyō-to): Japan's administrative system uses 都 as a special designation only for Tokyo. The four-tier prefecture system 都·道·府·県 (to, dō, fu, ken) has just one 都 (Tokyo), one 道 (Hokkaido), two 府 (Osaka, Kyoto), and 43 県 (regular prefectures). When a Japanese person says 都内 (tonai), they mean specifically "within Tokyo".

Kun-reading みやこ (miyako) — the elegant native word for "capital city".

Memory aid: people gathered (者) in a town (阝) — the urban capital.