京 means 'capital' and appears in several Chinese city names: 北京 (Northern Capital), 南京 (Southern Capital), 东京 (Eastern Capital - now the name for Tokyo in Japanese). 京剧 (Peking opera) also uses this character.
Top lid radical - the indexing component (Kangxi #8, often called the "lid" radical). Pictures the peaked roof of a tall watchtower. Anchors 京 in the family of elevated structures: 高 (tall), 亭 (pavilion), 亮 (bright).
Middle 口 - here a doorway or window in the watchtower wall, not a mouth. Together with the lid above and the legs below, the whole pictograph traces a tall fortified gate-tower of the ancient capital, from which 京 derives its "capital city" meaning.
Bottom 小-shape - historically the supporting pillars or legs of the watchtower, not the modern "small." Standalone 小 looks identical but carries no semantic load here; its job is to stabilize the tall structure above.
