You can picture inset as making a space in the surface of something and putting a smaller thing down into that space, so the small thing ends up level with the surface and counts as part of it. Nothing is stuck on top and nothing hangs off; the small thing is held inside. Once you can see that, the word works the same way whether the surface is a wooden lid, a ceiling, a ring, or the printed frame of a map — and it names both the act of putting the small thing in and the small thing itself.
The supplied Wiktionary entry traces inset to Middle English insetten, from Old English insettan 'to set in', which is simply in- plus set. The modern word still says exactly that: something is set in. This is a historical note, not a guess made from the picture above.
packet 裡的 Wiktionary 條目寫著：inset 來自中古英語 insetten，再往前是古英語 insettan（set in），也就是 in-（進去）加上 set（放置）。今天這個字說的還是同一件事——把東西放進去。這是來源說明，不是從上面那個畫面倒推出來的。
Wiktionary entry for “inset” supplied in this packet (kaikki extract, source_ref kaikki:3f6f69a190036ae4:184446988): “From Middle English insetten, from Old English insettan (‘to set in’), equivalent to in- + set.”
Two branches
嵌進表面：那個動作，和被嵌進去的那一塊
這一組最貼近核心畫面：真的有一個表面，真的有一塊東西被放進去。動詞講的是這個動作，名詞講的是做完之後留在那裡的那一塊。
verb · C1
To fix something into or onto the surface of another thing, so that it sits in that surface and becomes part of it, as when jewels are fixed into a box or lights are fixed into a ceiling.
鑲嵌；嵌入
嵌進大圖裡的小圖
同樣是「挖一塊、放進去」，只是表面換成了紙面或螢幕。小圖佔住大圖裡的一塊位置，兩張一起讀才完整。
noun · C1
A small picture, map, or diagram placed inside a larger one, usually in a corner, to show one part of it more closely or to add information the larger one cannot fit.
小插圖