で
de
で is not a place marker. It is the ground you act on.
The picture Laying down a field before anything happens. Everything then moves inside that field.
Where the picture shows up in で
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the ground you act on
会議室で待っています。
kaigi-shitsu de matte imasu
I'm waiting in the meeting room.
Just being somewhere takes に; doing something there takes で. 会議室にいます is only being in the room.
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the thing that carries you
バスで通っています。
basu de kayotte imasu
I commute by bus.
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what it is made out of
木で作りました。
ki de tsukurimashita
We made it out of wood.
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the cause it came out of
風邪で休みました。
kaze de yasumimashita
I took the day off with a cold.
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the span it fits inside
三十分で終わります。
sanjuppun de owarimasu
It'll be done in thirty minutes.