Agreed, the factories clearly aren't the same size as Manhattan.

But as a comparison of scale, both the airports in Denver and Dallas-Fort Worth are larger than Manhattan (27 mi2 or 70 km2).

https://en.wikipedia.org/wiki/Dallas_Fort_Worth_Internationa....

While that is a ton of activity (and empty space, if you have ever seen those airports), the Big Apple might not be the best reference for scale.