One way to hold this word: someone walks along the ground making marks, and from then on the two sides of those marks belong to different people. Every use keeps that shape — a line that was decided, then treated as real.
這個字可以想成有人沿著地面做記號，從此記號兩邊就分屬不同的人。它的每一種用法都保留這個形狀——一條被決定出來、然後被大家當真的線。
From the word’s history
Wiktionary records demarcation as entering English around 1752 from Spanish línea de demarcación / Portuguese linha de demarcação, the line the Pope laid down in 1493 dividing the New World between Spain and Portugal; demarcar is de- plus marcar, to mark. The marking is where the word starts.
根據 Wiktionary，demarcation 大約 1752 年進入英文，來自西班牙文 línea de demarcación、葡萄牙文 linha de demarcação——1493 年教宗畫下的那條線，把新世界分給西班牙和葡萄牙。demarcar 是 de- 加 marcar（做記號）。所以這個字從「做記號」開始，難怪今天的用法都圍著一條線打轉。
Wiktionary, "demarcation"
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