京 pictures a lofty structure on high ground — in oracle script, a watchtower on a mound. Height meant power, and the tallest towers stood where kings lived: the capital.
京 anchors 北京 (Northern Capital — Beijing, with 北 you learned) and 南京 (Southern Capital — Nanjing, with 南). China moved its capital many times, so the map is dotted with 京 names; even Tokyo (东京, Eastern Capital) borrowed the system. 京剧 is Peking opera — the capital's art. One character tells you where the emperor slept.
A watchtower on a mound — where the king lives: the CAPITAL.
Beijing, Nanjing, Tokyo — 'north capital', 'south capital', 'east capital': East Asia's great cities are compass points around 京.