The “edge of heaven and the corner of the sea” both refer to the remotest place. Hainan Island, located in the southernmost part of China, was considered the remotest place in ancient times. Su Shi, a famous poet of the Northern Song Dynasty, was exiled there in his later years. It is said that the two characters "Tian ya" (tiān yá 天涯) on a huge rock on the southernmost tip of the island were written by Su Shi.
This idiom refers to the remotest places or a very long distance between two people.

天的边缘（天涯），海的角落（海角），都是指非常遥远的地方。位于中国最南端的海南岛，自古以来被人们认为是“天涯海角”。北宋时代的大文学家苏轼，晚年被贬官来到这个地方。传说海南岛最南面巨石上的“天涯”两个字，就是苏轼写的。
这个成语用来形容极远的地方，或者两个人彼此相隔遥远。

天涯海角 (tiān yá hǎi jiǎo)
【翻译】The end of the sky and the corner of the sea.
【释义】涯：边。形容极远的地方，或相隔极远。
【例句】即便是天涯海角我也要跟随他。
【近义词】天南地北、天各一方
【反义词】近在咫尺、一衣带水