He cites from “the oldest known Vedic literature, Sri Brahma-samhita” [Discovered in the 16th century but there’s no mention of its date of composition]:
“The center of the divine lotus is the core — Krsna's residence… is mapped as a hexagonal mystic symbol [sat-konam]...The great mantra of eighteen syllables [Gopala-mantra], which is formed of six integral parts, is manifest as a hexagonal place with six-fold divisions.” [Sri Brahma-samhita, Ch-5, Tx-3]
“The core of that eternal holy abode which is called Gokula is the hexagonal land of Krsna's abode. [Sri Brahma-samhita, Ch-5, Tx-4]
According to Wikipedia [entry “Goloka”] Goloka is Krishna's heaven (souls return to the material world again and again to perfect themselves and go to Goloka). Etymology: “Goloka means the world of cows. The Sankrit word 'go' can refer to either cows or star”.