0 is nothing, non-existent, etc., so it represents not being in the building, where there is no floor (we call it ground)
It’s the first floor that you encounter of a building, not the zeroeth floor you encounter
Normal human convention is to count physical existing items from 1, I wouldn’t say I’m wearing 0 shirts right now at work for example, or that I’m wearing 1 shoe
Oh, you’re so close. Ground Zero is nothing, no elevation above or below ground level. The literal ground you walked on, into the building. You’re on ground level (outside) and then you’re on the ground floor (inside), as opposed to the American version where you suddenly “jump” to first floor once you’re in a building.
The first floor of a building is usually on a foundation, raising it above ground level
We call the thing you stand on outside ground and inside we call them floors, “ground floor” is silly
