capital, 10**16
京 centers on a grand central place: a capital city. The large-number sense (10^16) is a separate, specialized use that does not connect to the capital idea.
京 originally depicted a tall building or watchtower on a hill, representing a capital or large settlement. The modern form retains the top 亠 (roof) and the lower 口 and 小 as stylized remnants of the structure.
Picture a tall watchtower with a roof (亠) over a walled enclosure (口) and a small gate (小) below—this is the grand capital.
For キョウ, imagine the capital city of Kyoto (京都, きょうと): Kyoto -> キョウ, the heart of the capital.
Tokyo
Kyoto (city, prefecture)
imperial capital (esp. Kyoto)
Beijing (China); Peking
Tokyo Dome
going (up) to the capital; going to Tokyo
Nara
Nanjing (China); Nanking
University of Tokyo
Tokyo Electric Power
TV Tokyo
Kyoto University (abbr)
Nagoya (city)
Kyocera
Kyoto and Osaka; Kyoto-Osaka area
Keisei (train line Tokyo-Narita)
Saikyō Line (railway line running from Tokyo to Saitama)
Tokyo and Chiba
western capital; Kyoto
padlock