[hombre_fatal]

It's 67th in the world and less dense than 11 French cities, though not a great comparison because most of those are small cities. But just because it's in the top 100 doesn't mean it's maxed out. It still has 5000/sqkm fewer people than Paris.

Nor does it mean this trade off for a measly 10,000 flats is worth it in such a large city.

[Detrytus]

Please, the densities seen at the top of that list are really inhumane, more like prison camps than cities.

Also, increasing density might be easy if you demolish 100 single family homes to build 10 five-stories buildings, but replacing Barcelona's 5-6 stories blocks with 10-stories ones isn't going to be economically viable. And if some brave developer tries this, then the resulting apartments won't be cheap.