Each square in this blue map represents a small space, so 4 squares represent a room, and a door fits over 1 square.
https://cdn.masto.host/dicecamp/media_attachments/files/114/263/177/060/603/045/original/cf0c8b6d0e4d9a94.png
@icedquinn
The tradition is much older than WotC minis - TSR had it as standard.
Above-ground maps were massive, but underground maps much smaller.
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