sphere, circle, radius, range
圏 centers on a bounded area or conceptual domain: a sphere, circle, or range. The idea of a radius fits as the defining line of that bounded space.
圏 combines the enclosure 囗 with 巻 (roll, scroll), which likely contributes the sound and the idea of a bounded area. The character expresses a sphere or range.
The enclosure 囗 wraps around 巻 (scroll), like a scroll defining the boundary of a sphere or range. Picture a rolled-up map inside a box, marking the limits of a territory.
For ケン, imagine a ken (a Japanese prefecture) as a bounded sphere: ken -> ケン, and the enclosure 囗 marks its range.
sphere; circle; range; area; zone; bloc
inside (a region, area, etc.); within the range (of); within the sphere (of influence, etc.)
outside (a region, area, etc.); out of range (of a mobile network, radar, etc.); outside the sphere (of influence, etc.); out of contention; out of reach
the atmosphere
Arctic Circle; the Arctic
stratosphere
business region; marketing area; commercial sphere; trading area; region in which a business operates
Islamic world; Muslim world
Spanish-speaking world; Spanish-speaking countries
Soviet bloc
German-speaking countries; German language sphere
French-speaking world; francophone world; francophonie
eurozone; euro zone; euro area
Chūkyō metropolitan area (most of Aichi, and parts of Gifu and Mie prefectures; centered around Nagoya); Chūkyō region
sinophone world; Chinese-speaking world
Greater China (incl. Hong Kong, Macao, Taiwan and sometimes Singapore); Sinosphere
mesosphere
transient luminous event
circle of fifths
substratosphere