Low Density definition question.

[Orinsul]

So just a question.
Why are apartment blocks and department stores and other four or five story buildings in low density?
aren't they rather the definition of high density?

I've been assuming it's europe/america or somewhere having a different meanings for than I do?

 

[jcitron]

I think it's arbitrary because there's no medium density buildings which would fit what that size building should be, at least that's how I view it with smaller building being low density and very tall buildings, and those that hold a lot of CIMs, being high density.