These are looking at the densities of entire metropolitan areas, which doesn't mean much. In the NY-NJ metro area there are lots of high-density cities, like M

These are looking at the densities of entire metropolitan areas, which doesn't mean much. In the NY-NJ metro area there are lots of high-density cities, like Manhattan at 70,000/sq. mi.; Brooklyn, Union City, Hoboken, at 40,000/sq. mi.; Queens at 20,000/sq. mi. There is empty space between these cities, which lowers the density of the metro area, but that doesn't really matter. On the other hand, SV cities (Mountain View, Sunnyvale, San Jose), actually are at densities of 5,000-6,000/sq. mi. The figure we should actually be looking at is weighted population density, not population density.