For example on wikipedia for Switzerland it says the country has an area of 41,285 km². Does this take into account that a lot of that area is actually angled at a steep inclination, thus the actual surface area is in effect larger than what you would expect when looking onto a map in satellite view?
That’s a fun puzzle like “how many golf balls could you fit in a 747”, but to keep in line with the spirit of the original question, I think floor space is more in line with “is the area of a space more complicated than it’s 2D outline as seen from space” than walls are.
Does that sentence make any sense rereading it? It seems very confusing.