Several parts combine into one character.

市 originated as a pictograph of a market scene: a banner or flagpole rising above a gathered crowd, marking the site where buying and selling occurred. The character preserves the entire ancient East Asian marketplace in a few strokes — flag, gathering, exchange. From this concrete commercial scene grew the modern political meaning: market → urban gathering place → city. The semantic chain runs from "where commerce happens" to "where citizens dwell."

Korean reading "si." 都市 (dosi, city), 市場 (sijang, market — both physical marketplace and abstract economic market), 市民 (simin, citizen / resident of a city), 市內 (sinae, "inside the city" = urban area / downtown), 首爾市 (Seoul-si, Seoul Special City), 證市 (jeungsi, "stock market" — Korean term, while Mandarin uses 股市). Korean administrative geography uses 시 / 도 / 군 / 구 — 시 is the city tier above 군 county.

Mandarin shì, 4th tone. 市 (shì), 城市 (chéngshì, city), 市场 (shìchǎng, market), 市民 (shìmín, citizen), and 股市 (gǔshì, "stock-market" = stock exchange — major financial vocabulary). Plus the wonderfully evocative 超市 (chāoshì, "super-market" = supermarket — Mandarin's direct calque of the English "supermarket" using 超 super + 市 market). 超市 became a defining feature of post-1990s Chinese urban shopping.

Japanese on-reading シ (shi) — 市 (shi, city — used as suffix on city names: 大阪市 Ōsaka-shi, 福岡市 Fukuoka-shi), 都市 (toshi, city / metropolis), 市民 (shimin, citizen), 市役所 (shiyakusho, city office). Kun-reading いち (ichi) — 市場 (ichiba, physical marketplace) — and here Japanese makes a beautiful semantic distinction: 市場 read as いちば (ichiba) = the physical produce market or fish market (where you walk among stalls), while 市場 read as しじょう (shijō) = abstract market (stock market, currency market, market segment). Same kanji, different readings, different concepts. 朝市 (asaichi, morning market) is a Japanese local-tourism staple.

Memory aid: a banner over a marketplace gathering — where commerce concentrated, cities formed.