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?
Ok, so I know this is just a joke, but you got me thinking.
Each floor of a skyscaper with an area of x² ft, is an additional x² ft of unique space. An acre of skyscrapers, could have 20-30 times more useable square footage than an acre of farmland.
It is a near future concept of a fully self sufficient megacity, a sort of intermediate stage towards an ecumenopolis (a planet entirely urbanized with an extreme population density). One popular example would be coruscant, the capital world of the galaxy in star wars.
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.